Effect of perfluorocarbons on brain oxygenation and ischemic damage in an acute subdural hematoma model in rats

Enduring Neuroprotective Effect of Subacute Neural Stem Cell Transplantation After Penetrating TBI

Traumatic brain injury (TBI) is the largest cause of death and disability of persons under 45 years old, worldwide. Independent of the distribution, outcomes such as disability are associated with huge societal costs. The heterogeneity of TBI and its complicated biological response have helped clarify the limitations of current pharmacological approaches to TBI management. Five decades of effort have made some strides in reducing TBI mortality but little progress has been made to mitigate TBI-induced disability. Lessons learned from the failure of numerous randomized clinical trials and the inability to scale up results from single center clinical trials with neuroprotective agents led to the formation of organizations such as the Neurological Emergencies Treatment Trials (NETT) Network, and international collaborative comparative effectiveness research (CER) to re-orient TBI clinical research. With initiatives such as TRACK-TBI, generating rich and comprehensive human datasets with demographic, clinical, genomic, proteomic, imaging, and detailed outcome data across multiple time points has become the focus of the field in the United States (US). In addition, government institutions such as the US Department of Defense are investing in groups such as Operation Brain Trauma Therapy (OBTT), a multicenter, pre-clinical drug-screening consortium to address the barriers in translation. The consensus from such efforts including “The Lancet Neurology Commission” and current literature is that unmitigated cell death processes, incomplete debris clearance, aberrant neurotoxic immune, and glia cell response induce progressive tissue loss and spatiotemporal magnification of primary TBI. Our analysis suggests that the focus of neuroprotection research needs to shift from protecting dying and injured neurons at acute time points to modulating the aberrant glial response in sub-acute and chronic time points. One unexpected agent with neuroprotective properties that shows promise is transplantation of neural stem cells. In this review we present (i) a short survey of TBI epidemiology and summary of current care, (ii) findings of past neuroprotective clinical trials and possible reasons for failure based upon insights from human and preclinical TBI pathophysiology studies, including our group's inflammation-centered approach, (iii) the unmet need of TBI and unproven treatments and lastly, (iv) present evidence to support the rationale for sub-acute neural stem cell therapy to mediate enduring neuroprotection.

Preclinical Validation of the Therapeutic Potential of Glasgow Oxygen Level Dependent (GOLD) Technology: a Theranostic for Acute Stroke

In acute stroke patients, penumbral tissue is non-functioning but potentially salvageable within a time window of variable duration and represents target tissue for rescue. Reperfusion by thrombolysis and/or thrombectomy can rescue penumbra and improve stroke outcomes, but these treatments are currently available to a minority of patients. In addition to the utility of Glasgow Oxygen Level Dependent (GOLD) as an MRI contrast capable of detecting penumbra, its constituent perfluorocarbon (PFC) oxygen carrier, combined with normobaric hyperoxia, also represents a potential acute stroke treatment through improved oxygen delivery to penumbra. Preclinical studies were designed to test the efficacy of an intravenous oxygen carrier, the perfluorocarbon emulsion Oxycyte® (O-PFC), combined with normobaric hyperoxia (50% O₂) in both in vitro (neuronal cell culture) and in vivo rat models of ischaemic stroke. Outcome was assessed through the quantification of lipid peroxidation and oxidative stress levels, mortality, infarct volume, neurological scoring and sensorimotor tests of functional outcome in two in vivo models of stroke. Additionally, we investigated evidence for any positive or negative interactions with the thrombolytic recombinant tissue plasminogen activator (rt-PA) following embolus-induced stroke in rats. Treatment with intravenous O-PFC + normobaric hyperoxia (50% O₂) provided evidence of reduced infarct size and improved functional recovery. It did not exacerbate oxidative stress and showed no adverse interactions with rt-PA. The positive results and lack of adverse effects support human trials of O-PFC + 50% O₂ normobaric hyperoxia as a potential therapeutic approach. Combined with the diagnostic data presented in the preceding paper, O-PFC and normobaric hyperoxia is a potential theranostic for acute ischaemic stroke.

Microdialysis as Clinical Evaluation of Therapeutic Hypothermia in Rat Subdural Hematoma Model

Cerebral microdialysis (MD) is a fine laboratory technique which has been established for studying physiological, pharmacological, and pathological changes in the experimental studies of traumatic brain injury (TBI). This technique has also been well translated and widely applied to clinical bedside monitoring to provide pathophysiological analysis in severe TBI patients. The MD technique is thus well suited for straightforward translation from basic science to clinical application.In this chapter, we describe our evaluation of MD method in acute subdural hematoma (ASDH) rat model. With 100 kDa cut-off microdialysis membrane, we could measure several biomarkers such as ubiquitin carboxy hydrolase L1 (UCH-L1), a neuronal marker and glial fibrillary acidic protein (GFAP), and a glial marker in extracellular fluid. In this experiment, we could detect that the peak of extracellular UCH-L1 in the early hypothermia group was significantly lower than in the normothermia group. Also, in the late phase of reperfusion (>2.5 h after decompression), extracellular GFAP in the early hypothermia group was lower than in the normothermia. These data thus suggested that early, preoperatively induced hypothermia could mediate the reduction of neuronal and glial damage in the reperfusion phase of ischemia/reperfusion brain injury.Microdialysis allows for the direct measurement of extracellular molecules in an attempt to characterize metabolic derangements before they become clinically relevant. Advancements in technology have allowed for the bedside assay of multiple markers of ischemia and metabolic dysfunction, and the applications for traumatic brain injury have been well established. As clinicians become more comfortable with these tools their widespread use and potential for clinical impact with continue to rise.

Evidence to support mitochondrial neuroprotection, in severe traumatic brain injury

Traumatic brain injury (TBI) is still the leading cause of disability in young adults worldwide. The major mechanisms - diffuse axonal injury, cerebral contusion, ischemic neurological damage, and intracranial hematomas have all been shown to be associated with mitochondrial dysfunction in some form. Mitochondrial dysfunction in TBI patients is an active area of research, and attempts to manipulate neuronal/astrocytic metabolism to improve outcomes have been met with limited translational success. Previously, several preclinical and clinical studies on TBI induced mitochondrial dysfunction have focused on opening of the mitochondrial permeability transition pore (PTP), consequent neurodegeneration and attempts to mitigate this degeneration with cyclosporine A (CsA) or analogous drugs, and have been unsuccessful. Recent insights into normal mitochondrial dynamics and into diseases such as inherited mitochondrial neuropathies, sepsis and organ failure could provide novel opportunities to develop mitochondria-based neuroprotective treatments that could improve severe TBI outcomes. This review summarizes those aspects of mitochondrial dysfunction underlying TBI pathology with special attention to models of penetrating traumatic brain injury, an epidemic in modern American society.

Neuroprotective effects of perflurocarbon (oxycyte) after contusive spinal cord injury

Spinal cord injury (SCI) often results in irreversible and permanent neurological deficits and long-term disability. Vasospasm, hemorrhage, and loss of microvessels create an ischemic environment at the site of contusive or compressive SCI and initiate the secondary injury cascades leading to progressive tissue damage and severely decreased functional outcome. Although the initial mechanical destructive events cannot be reversed, secondary injury damage occurs over several hours to weeks, a time frame during which therapeutic intervention could be achieved. One essential component of secondary injury cascade is the reduction in spinal cord blood flow with resultant decrease in oxygen delivery. Our group has recently shown that administration of fluorocarbon (Oxycyte) significantly increased parenchymal tissue oxygen levels during the usual postinjury hypoxic phase, and fluorocarbon has been shown to be effective in stroke and head injury. In the current study, we assessed the beneficial effects of Oxycyte after a moderate-to-severe contusion SCI was simulated in adult Long-Evans hooded rats. Histopathology and immunohistochemical analysis showed that the administration of 5 mL/kg of Oxycyte perfluorocarbon (60% emulsion) after SCI dramatically reduced destruction of spinal cord anatomy and resulted in a marked decrease of lesion area, less cell death, and greater white matter sparing at 7 and 42 days postinjury. Terminal deoxynucleotidyl transferase dUTP nick end labeling staining showed a significant reduced number of apoptotic cells in Oxycyte-treated animals, compared to the saline group. Collectively, these results demonstrate the potential neuroprotective effect of Oxycyte treatment after SCI, and its beneficial effects may be, in part, a result of reducing apoptotic cell death and tissue sparing. Further studies to determine the most efficacious Oxycyte dose and its mechanisms of protection are warranted.

The intravenous perfluorocarbon emulsion Oxycyte does not increase hyperbaric oxygen-related seizures in a non-sedated swine model

PURPOSE

Standard treatment for decompression sickness (DCS) is recompression therapy with hyperbaric oxygen (HBO). Non-recompressive therapies are needed to address mass casualty scenarios such as a disabled submarine rescue or DCS therapy in remote environments. Intravenously delivered perfluorocarbon (PFC) emulsions improve blood oxygen content and decrease mortality in several animal models of DCS. However, the enhanced oxygen delivery of PFC emulsions may increase CNS oxygen toxicity (seizures) risk when used in conjunction with HBO. We studied seizure latency and duration in swine randomized to receive PFC or normal saline with 6 ATA of oxygen.

METHODS

Yorkshire swine (n = 31) were fitted with EEG electrodes and randomized to receive 5 ml/kg of the PFC Oxycyte (Oxygen Biotherapeutics Inc., Morrisville, NC) or saline intravenously 1 h before HBO. Unsedated animals were fitted with a snout mask for inhaled gas delivery, positioned inside the hyperbaric chamber, and compressed to 165 ft of sea water (6 ATA). After 2.5 min at 6 ATA, breathing gas was switched to 100 % O2 until signs of seizure were observed and EEG activity was evident. At seizure onset gas was switched back to air for 3 min, then the chamber was decompressed. After 24 h, the dive profile/oxygen exposure was repeated to ensure no secondary effects of PFC drug redistribution or emulsion metabolism.

RESULTS/CONCLUSION

Intravenous PFC emulsion did not decrease seizure latency or increase duration on initial HBO exposure or after 24 h. This finding demonstrates the safety of PFC use in conjunction with recompression therapy to treat DCS.

Perfluorocarbons enhance a T2*-based MRI technique for identifying the penumbra in a rat model of acute ischemic stroke

Accurate imaging of ischemic penumbra is crucial for improving the management of acute stroke patients. T2* magnetic resonance imaging (MRI) combined with a T2*oxygen challenge (T2*OC) is being developed to detect penumbra based on changes in blood deoxyhemoglobin. Using 100% O2, T2*OC-defined penumbra exhibits ongoing glucose metabolism and tissue recovery on reperfusion. However, potential limitations in translating this technique include a sinus artefact in human scans with delivery of 100% OC and relatively small signal changes. Here we investigate whether an oxygen-carrying perfluorocarbon (PFC) emulsion can enhance the sensitivity of the technique, enabling penumbra detection with lower levels of inspired oxygen. Stroke was induced in male Sprague-Dawley rats (n=17) with ischemic injury and perfusion deficit determined by diffusion and perfusion MRI, respectively. T2* signal change was measured in regions of interest (ROIs) located within ischemic core, T2*OC-defined penumbra and equivalent contralateral areas during 40% O2±prior PFC injection. Region of interest analyses between groups showed that PFC significantly enhanced the T2* response to 40% O2 in T2*-defined penumbra (mean increase of 10.6±2.3% compared to 5.6±1.5% with 40% O2, P<0.001). This enhancement was specific to the penumbra ROI. Perfluorocarbon emulsions therefore enhances the translational potential of the T2*OC technique for identifying penumbra in acute stroke patients.

Preoperative-induced mild hypothermia attenuates neuronal damage in a rat subdural hematoma model

Post-traumatic hypothermia has been effective for traumatic brain injury in the laboratory setting. However, hypothermia has not shown efficacy in clinical trials. With the results of a recent clinical trial, we hypothesized that hypothermia might reduce neuronal damage in acute subdural hematoma (ASDH) by blunting the effects of reperfusion injury. Twenty rats were induced with ASDH and placed into one of four groups. The normothermia group was maintained at 37 °C throughout. In the early hypothermia group, brain temperature was reduced to 33 °C 30 min prior to craniotomy. In the late hypothermia group, brain temperature was lowered to 33 °C 30 min after decompression. The sham group had no ASDH and underwent only craniotomy with normothermia. For estimation of glial and neuronal cell damage, we analyzed serum and microdialysate (using a 100kD probe) concentrations of: glial fibrillary acidic protein (GFAP) and ubiquitin carboxyl--terminal hydrolase -L1 (UCH-L1). Hypothermia induced early significantly reduced the concentration of MD UCH-L1. In conclusion, hypothermia induced early may reduce neuronal cell damage in the reperfusion injury, which was induced after ASDH removal. MD UCH-L1 seems like a good -candidate for a sensitive microdialysate biomarker for -neuronal injury and outcome.

Effect of transpleural perfusion with oxygenated perfluorocarbon in a rat model of acute lung injury

BACKGROUND

Despite advances in critical care, more effective methods of systemic oxygenation in patients with acute lung injury or acute respiratory distress syndrome are needed. The goal of this study was to determine if it is possible to increase systemic oxygenation by transpleural perfusion with oxygenated perfluorocarbon in animals with induced acute lung injury.

METHODS

Eighteen Sprague-Dawley rats were intubated, and acute lung injury was induced by aspiration of 0.1N HCl (1 mL/kg) through the tracheal tube. Inflow and outflow tubes were placed in the thoracic cavity and connected to a perfusion circuit containing a roller pump, warmer, and oxygenator. Rats in group I were not treated after aspiration of HCl, those in group II were perfused with oxygenated saline, and those in group III were perfused with oxygenated perfluorocarbon. Arterial blood gases were collected every 30 minutes for 180 minutes. At the last step of the experiments, pathological examination of the lungs and parietal pleura was performed.

RESULTS

PaO(2) in group III was significantly higher than that in group I or II. PaCO(2) in group III was significantly lower than that in the other two groups. Histological examination showed relatively well-delineated zones of inflammation-free coagulative necrosis of lung parenchyma in all groups.

CONCLUSIONS

Transpleural perfusion with oxygenated perfluorocarbon in an animal model of induced acute lung injury resulted in a significant increase in systemic oxygenation and depletion of systemic carbon dioxide, and might be a useful method for improving systemic oxygenation in patients with acute lung injury.

Neuroprotective effect of preoperatively induced mild hypothermia as determined by biomarkers and histopathological estimation in a rat subdural hematoma decompression model

OBJECT

In patients who have sustained a traumatic brain injury (TBI), hypothermia therapy has not shown efficacy in multicenter clinical trials. Armed with the post hoc data from the latest clinical trial (National Acute Brain Injury Study: Hypothermia II), the authors hypothesized that hypothermia may be beneficial in an acute subdural hematoma (SDH) rat model by blunting the effects of ischemia/reperfusion injury. The major aim of this study was to test the efficacy of temperature management in reducing brain damage after acute SDH.

METHODS

The rats were induced with acute SDH and placed into 1 of 4 groups: 1) normothermia group (37°C); 2) early hypothermia group, head and body temperature reduced to 33°C 30 minutes prior to craniotomy; 3) late hypothermia group, temperature lowered to 33°C 30 minutes after decompression; and 4) sham group, no acute SDH (only craniotomy with normothermia). To assess for neuronal and glial cell damage, the authors analyzed microdialysate concentrations of GFAP and ubiquitin carboxyl-terminal hydrolase-L1 (UCH-L1) by using a 100-kD probe. Fluoro-Jade B-positive neurons and injury volume with 2,3,5-triphenyltetrazolium chloride staining were also measured.

RESULTS

In the early phase of reperfusion (30 minutes, 2.5 hours after decompression), extracellular UCH-L1 in the early hypothermia group was significantly lower than in the normothermia group (early, 4.9 ± 1.0 ng/dl; late, 35.2 ± 12.1 ng/dl; normothermia, 50.20 ± 28.3 ng/dl; sham, 3.1 ± 1.3 ng/dl; early vs normothermia, p < 0.01; sham vs normothermia, p < 0.01, analyzed using ANOVA followed by a post hoc Bonferroni test). In the late phase of reperfusion (> 2.5 hours after decompression), extracellular GFAP in the early hypothermia group was also lower than in the normothermia and late hypothermia groups (early, 5.5 ± 2.9 ng/dl; late, 7.4 ± 3.4 ng/dl; normothermia, 15.3 ± 8.4 ng/dl; sham, 3.3 ± 1.0 ng/dl; normothermia vs sham; p < 0.01). The number of Fluoro-Jade B-positive cells in the early hypothermia group was significantly smaller than that in the normothermia group (normothermia vs early: 774,588 ± 162,173 vs 180,903 ± 42,212, p < 0.05). Also, the injury area and volume were smaller in the early hypothermia group in which hypothermia was induced before craniotomy and cerebral reperfusion (early, 115.2 ± 15.4 mm(3); late, 344.7 ± 29.1 mm(3); normothermia, 311.2 ± 79.2 mm(3); p < 0.05).

CONCLUSIONS

The data suggest that early, preoperatively induced hypothermia could mediate the reduction of neuronal and glial damage in the reperfusion phase of ischemia/reperfusion brain injury.

Improvement of oxygen supply by an artificial carrier in combination with normobaric oxygenation decreases the volume of tissue hypoxia and tissue damage from transient focal cerebral ischemia

Tissue hypoxia may play an important role in the development of ischemic brain damage. In the present study we investigated in a rat model of transient focal brain ischemia the neuroprotective effects of increasing the blood oxygen transport capacity by applying a semifluorinated alkane (SFA)-containing emulsion together with normobaric hyperoxygenation (NBO). The spread of tissue hypoxia was studied using pimonidazole given prior to filament-induced middle cerebral artery occlusion (MCAO, 2 h). Treatment consisted of intravenous injection of saline or the SFA-containing emulsion (0.5 or 1.0 ml/100g body weight; [SFA(0.5) or SFA(1.0)]) either upon establishing MCAO (early treatment) or after filament removal (delayed treatment). After injection NBO was administered for 8 h (early treatment) or 6 h (delayed treatment). Experiments were terminated 8 or 24 h after MCAO. In serial brain sections tissue hypoxia and irreversible cell damage were quantitatively determined. Furthermore, we studied hypoxia-related gene expression (VEGF, flt-1). Early treatment significantly (p<0.05) reduced the volumes of tissue damage (8 h after MCAO: SFA(1.0), 57±34 mm³; controls, 217±70 mm³; 24 h after MCAO: SFA(1.0), 189±82 mm³; controls, 317±60 mm³) and of P-Add immunoreactivity (8 h after MCAO: SFA(1.0), 261±37 mm³; controls, 339±26 mm³; 24h after MCAO: SFA(1.0), 274±47 mm³; controls, 364±46 mm³). Delayed treatment was comparably successful. The volume of the hypoxic penumbra was not decreased by the treatment. Similarly, VEGF and flt-1 mRNA levels did not differ between the experimental groups. From these data we conclude that increasing the blood oxygen transport capacity in the plasma compartment provides a neuroprotective effect by alleviating the severity of hypoxia to a level sufficient to prevent cells from transition into irreversible damage.

Perfluorocarbon emulsions as a promising technology: a review of tissue and vascular gas dynamics

Perfluorocarbon (PFC) emulsions are halogen-substituted carbon nonpolar oils with resultant enhanced dissolved respiratory gas (O(2), N(2), CO(2), nitric oxide) capabilities. In the first demonstration of enhanced O(2) solubility, inhaled PFC could sustain rat metabolism. Intravenous emulsions were then trialed as "blood substitutes." In the last 10 yr, biocomputational modeling has enhanced our mechanistic understanding of PFCs. Contemporary research is now taking advantage of these physiological discoveries and applying PFCs as "oxygen therapeutics," as well as ways to enhance other gas movements. One particularly promising area of research is the treatment of gas embolism (arterial and venous emboli/decompression sickness). An expansive understanding of PFC-enhanced diffusive gas movements through tissue and vasculature may have analogous applications for O(2) or other respiratory gases and should provide a revolution in medicine. This review will stress the fundamental knowledge we now have regarding how respiratory gas movements are changed when intravenous PFC is present.

Perfluorocarbon emulsions improve cognitive recovery after lateral fluid percussion brain injury in rats

OBJECTIVE

Perfluorocarbon emulsions have been shown to improve outcomes in stroke models. This study examined the effect of Oxycyte, a third-generation perfluorocarbon emulsion (04RD33; Synthetic Blood International, Inc., Costa Mesa, CA) treatment on cognitive recovery and mitochondrial oxygen consumption after a moderate lateral fluid percussion injury (LFPI).

METHODS

Adult male Sprague-Dawley rats (Harlan Bioproducts for Science, Indianapolis, IN) were allocated to 4 groups: 1) LFPI treated with a lower dose of Oxycyte (4.5 mL/kg); 2) LFPI with a higher dose of Oxycyte (9.0 mL/kg); 3) LFPI with saline infusion; and 4) sham animals treated with saline. Fifteen minutes after receiving moderate LFPI or sham surgery, animals were infused intravenously with Oxycyte or saline within 30 minutes while breathing 100% O2. Animals breathed 100% O2 continuously for a total of 4 hours after injury. At 11 to 15 days after LFPI, animals were assessed for cognitive deficits using the Morris water maze test. They were sacrificed at Day 15 after injury for histology to assess hippocampal neuronal cell loss. In a parallel study, mitochondrial oxygen consumption values were measured by the Cartesian diver microrespirometer method.

RESULTS

We found that injured animals treated with a lower or higher dose of Oxycyte had significant improvement in cognitive function when compared with injured saline-control animals (P < 0.05). Moreover, injured animals that received either dose of Oxycyte had significantly less neuronal cell loss in the hippocampal CA3 region compared with saline-treated animals (P < 0.05). Furthermore, a lower dose of Oxycyte significantly improved mitochondrial oxygen consumption levels (P < 0.05).

CONCLUSION

The current study demonstrates that Oxycyte can improve cognitive recovery and reduce CA3 neuronal cell loss after traumatic brain injury in rats.

Reduction of hypoxia by perfluorocarbon emulsion in a traumatic spinal cord injury model

Object

Few therapies have consistently demonstrated effectiveness in preserving O2 delivery after spinal cord injury (SCI). Perfluorocarbons (PFCs) offer great promise to carry and deliver O2 more efficiently than conventional measures. The authors investigated the use of Clark-type microelectrodes to monitor spinal cord oxygenation directly (intraparenchymal [IP] recording) and indirectly (cerebrospinal fluid [CSF] recording) in the context of SCI, O2 therapy, and PFC treatment.

Methods

After placement of a subdural/CSF Licox probe in rats, incremental increases in the fraction of inspired O2 (FiO2) up to 100% were administered to establish a dose-response curve. The probe was then placed in the parenchyma of the same animals for a second dose-response curve. In a second study, rats with CSF or IP probes underwent SCI with the NYU Impactor and treatment with O2, followed by administration of PFC, or saline in the control group.

Results

All animals in the first experiment responded to the FiO2 dose increase, with changes in PO2 evident in both CSF and IP levels. The SCI in the second experiment caused a marked drop in PO2 from a mean of 21.4 to 10.4 mm Hg, with most animals dropping to less than half their preinjury value. All animals responded to 100% O2 treatment. Every animal that received PFCs showed significant improvement, with a mean increase in PO2 of 23.3 mm Hg. Only 1 saline-treated animal showed any benefit. Oxygen values in the PFC treatment group reached up to 6 times the normal level.

Conclusions

Oxygen levels in SCI show a profound drop almost immediately postinjury. Administration of PFCs combined with 100% O2 therapy can reverse tissue hypoxia and holds promise for reducing ischemic injury.