Focal cerebral ischemia: reduction in size of infarcts by ventriculo-subarachnoid perfusion with fluorocarbon emulsion

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.

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.

Reduction of cerebral infarction using the third circulation

OBJECTIVE

To ascertain whether ventriculosubarachnoid perfusion of the brain with an oxygen-carrying nutrient emulsion affects the volume of infarction in animals with permanent middle cerebral artery occlusion.

DESIGN

Prospective, randomized, controlled trial.

SETTING

An animal laboratory in a university setting.

SUBJECTS

Twenty-eight closed colony adult cats weighing between 3.5 and 4.5 kg.

INTERVENTIONS

Cats were assigned randomly into one of three groups: untreated surgical controls, artificial cerebrospinal fluid (ACSF) perfused, or oxygenated fluorochemical (t-bis perfluorobutylethylene; F44E) nutrient emulsion (OFNE) perfused. The formulation used in this study was developed for clinical use and is currently being used in a phase 1 clinical trial in patients with severe ischemic stroke. Focal cerebral ischemia was induced by permanently clipping the middle cerebral artery via the retro-orbital approach. Treatment was initiated 90 mins postocclusion and continued for 18 hrs. Animals were killed 1 hr after the termination of perfusion, the brains were sectioned and stained with 2,3,5-triphenyltetrazolium chloride, and the infarct area was determined with a computer digitizer.

MEASUREMENTS AND MAIN RESULTS

There was a significant difference in cerebral infarct volume in the OFNE-perfused animals compared with the other groups ( p<or=.015). Intracranial pressure was significantly reduced in the OFNE-perfused group relative to the surgical control group at 18 hrs ( P<or=.05). Overall, infarct volume correlated with intracranial pressure measured at the end of the treatment period (Spearman rank order, p<.001).

CONCLUSIONS

Fluorochemical emulsion delivery of oxygen and nutrients directly to the brain by means of ventriculocisternal perfusion is a viable treatment alternative for cerebral ischemia. In addition, this technique may control elevations in intracranial pressure following stroke.

Quantitative assessment of ischemic pathology in axons, oligodendrocytes, and neurons: attenuation of damage after transient ischemia

Axons and oligodendrocytes are vulnerable to cerebral ischemia. The absence of quantitative methods for assessment of white matter pathology in ischemia has precluded in vivo evaluation of therapeutic interventions directed at axons and oligodendrocytes. The authors demonstrate here that the quantitative extent of white matter pathology was reduced by restoration of cerebral blood flow after 2 hours of middle cerebral artery occlusion. Focal ischemia was induced in anesthetized rats by intraluminal thread placement, either transiently (for 2 hours) or permanently. At 24 hours after induction of ischemia, axonal damage was determined by amyloid precursor protein (APP) immunohistochemistry, and the ischemic insult to oligodendrocytes was assessed by Tau-1 immunostaining in the same sections. In adjacent sections, ischemic damage to neuronal perikarya was defined histologically. The hemispheric extent of axonal damage was reduced by 70% in the transiently occluded animals from that in permanently occluded animals. The volumes of oligodendrocyte pathology and of neuronal perikaryal damage were reduced by 62% and 58%, respectively, in the transiently occluded animals. These results demonstrate that this methodologic approach for assessing ischemic damage in axons and oligodendrocytes can detect relative alterations in gray and white matter pathology with intervention strategies.

Perfluorocarbons: recent developments and implications for neurosurgery

Over the last 30 years, perfluorocarbons (PFCs) have been extensively investigated as oxygen carriers. Early studies indicated that these compounds could be used as blood substitutes or protective agents against ischemia. Adverse characteristics such as instability, short intravascular half-life, and uncertainties concerning possible toxicity precluded wide clinical application. However, advances in PFC technology have led to the development of improved second-generation oxygen carriers that incorporate well-tolerated emulsifiers (egg-yolk phospholipids). The authors review recent developments in this field and consider the potential role of PFCs in future neurosurgical practice. Diagnostic applications could include their use to assess cerebral blood flow, local oxygen tension, and brain metabolism or to achieve enhanced imaging and precise staging of inflammatory, neoplastic, or vascular disease processes by means of computerized tomography, ultrasonography, and magnetic resonance studies. Therapeutic applications could include cerebral protection, an adjunctive role in radiotherapy of malignant brain tumors, protection against air embolism, the preservation of organs for transplantation, and ventilatory support in head-injured patients with compromised lung function. In addition, PFCs have been used successfully as a tool in ophthalmic microsurgery and potentially they could fulfill a similar role in microneurosurgery.

The perfluorocarbon fluoromethyloadamantane offers cerebral protection in a model of isovolemic hemodilution in rabbits

BACKGROUND AND PURPOSE

Perfluorocarbons (PFCs) are considered promising cerebral protection agents because they could combine the beneficial effects of decreased blood viscosity with enhanced oxygen-carrying capacity and oxygen tissue delivery, but trials of PFCs as hemodilutants have been very limited. We evaluated fluoromethyloadamantane (FMA), a new perfluorocarbon compound, as an isovolemic hemodilutant and compared it with low-molecular-weight dextran 40 (D40) and a control group.

METHODS

Through a transorbital craniectomy, the internal carotid, anterior, and middle cerebral arteries were coagulated to create a cerebral infarction in anesthetized, mechanically ventilated rabbits. No other experimental procedure was performed in control animals. In the two other groups, hemodilution was commenced 30 minutes after the arterial occlusion with either D40 or FMA. Hemodynamic parameters and brain and systemic temperature were monitored throughout the experiments. All animals were killed 6 hours after the arterial occlusion.

RESULTS

Hemodynamic and metabolic parameters and blood oxygen content were not affected by the infusion of either FMA or D40. Brain and systemic temperature remained constant. The ratio of infarct volume to the hemispheric volume was 19.6 +/- 3.7% in the FMA group (n = 17), 19.9 +/- 4.6% in the D40 group (n = 16), and 40.3 +/- 5.7% in the control group (n = 17). The difference in infarct volume of both FMA and D40 animals compared with controls was statistically significant (P < .01) when tested with Student's t test. There was no significant difference between FMA and D40 groups.

CONCLUSIONS

These results suggest that FMA has cerebral protective properties and should be purified, optimized, and further tested experimentally to develop a stable, efficient, and safe oxygen carrier, potentially suitable for clinical trials.

A novel treatment for ischemic intracranial hypertension in cats

There is no accepted efficacious treatment for ischemic cerebral edema. We show in a cat model of focal cerebral ischemia that infarct volume can be reduced (p less than 0.05) by ventriculocisternal perfusion with an oxygenated fluorochemical emulsion (bis-perfluorobutylethylene). An accompanying effect of such ventriculocisternal perfusion is a reduction in intracranial pressure. At 18 hours following the start of the perfusion, there was a significant (p less than 0.05) difference in intracranial pressure between nonperfused controls (mean 11.4 [range 2.3-23.0] torr, n = 6) and cats perfused with an oxygenated nutrient solution not containing fluorochemical (mean 11.3 [range 3.0-29.0] torr, n = 8) or animals perfused with the oxygenated fluorochemical emulsion (mean 2.21 [range 0-3.5] torr, n = 7). Perfusion with this oxygenated fluorochemical emulsion warrants further study as a treatment for elevated intracranial pressure.

Perfluorochemical oxygen carriers and ischaemic tissues

This paper has outlined the potential beneficial effects of emulsified PFCs for ischaemic tissue rescue. There are very strong indications that PFC emulsions will come to play an important part in the management of the ischaemic tissues. However, the immediate goal of future studies should be to assess the value of improved formulations in this context together with analysis of their mechanism(s) of action, both alone and in combination with other therapeutic agents.

Enhancement of the Arthus reaction and suppression of delayed type hypersensitivity (DTH) by pluronic F-68, a detergent frequently used to prepare perfluorocarbon emulsions

The effect of a 20% w/v RM101 (perfluorobutyltetrahydrofuran) emulsion containing 5% w/v of the detergent Pluronic F-68 or 5% w/v Pluronic F-68 given alone on the Arthus reaction and on delayed type hypersensitivity (DTH) were evaluated in female A/J mice. The test substances were administered i.v. at 1% body weight at 0,4,7,14 and 28 days prior to the i.p. immunization with 10(7) sheep red blood cells (SRBC). The increase in footpad swelling at 4 h (Arthus reaction) and at 24 h (DTH) after elicitation with the s.c. administration of 10(8) SRBC into the left footpad was used to assess immune competence. Pluronic F-68 given alone enhanced the Arthus reaction only when administered on day 0 of immunization. Pluronic F-68 given alone, as well as the perfluorocarbon emulsion containing Pluronic F-68, suppressed the 24 h DTH for as long as 4 days prior to immunization. Nonemulsified perfluorocarbon, on the other hand, had no effect on either the Arthus reaction or on DTH. The immunostimulatory agent, levamisole, administered (10 mg/kg i.p.) 1.5-2 h prior to immunization with SRBC counteracted both the Arthus reaction and the DTH response produced by Pluronic F-68. The present data clearly demonstrate that the changes in Arthus reaction and the DTH response are due to the Pluronic F-68 used to emulsify the RM101 perfluorocarbon; the changes induced by the detergent in these two immune parameters probably involve separate mechanisms.

The glutamate antagonist MK-801 reduces focal ischemic brain damage in the rat

Excessive activation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor has been implicated in the sequence of neurochemical events that results in irreversible neuronal damage in cerebral ischemia. The effects of the NMDA antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) upon the amount of ischemic brain damage has been assessed quantitatively in the lightly anesthetized rat. Focal cerebral ischemia was produced by the permanent occlusion of one middle cerebral artery (MCA), and the animals were killed 3 hours after the arterial occlusion. MK-801 (0.5 mg/kg) was administered intravenously either 30 minutes prior to MCA occlusion or 30 minutes after the induction of ischemia. Pretreatment with MK-801 reduced the volume of ischemic damage both in the cerebral cortex (by 38% compared with untreated rats with MCA occlusion; p less than 0.01) and in the caudate nucleus (by 18% compared with controls; p less than 0.05). Treatment with MK-801, initiated 30 minutes after MCA occlusion, reduced the volume of ischemic damage in the cerebral cortex (by 52% compared with controls; p less than 0.01). The volume of ischemic damage in the caudate nucleus was minimally influenced by MK-801 treatment initiated after MCA occlusion. The antiischemic effects of MK-801 were readily demonstrable despite the hypotension that MK-801 induced in rats anesthetized with halothane (0.5%), nitrous oxide (70%), and oxygen (30%). The potency of MK-801 in reducing ischemic brain damage, even when administered after the induction of ischemia, highlights the potential use of NMDA receptor antagonists for the treatment of focal cerebral ischemia in humans.

Quantitation of photochemically induced focal cerebral ischemia in the rat

This study was carried out with a recently developed model of focal cerebral ischemia in the rat based on the photochemical induction of thrombotic stroke using the dye Rose Bengal. We examined the change in the volume of the lesion and brain water content, in separate groups of rats, at different times (1, 4, 24, 72, and 168 h) after the induction of the ischemic lesion. The volume of ischemic damage increased rapidly between 1 and 24 h after the ischemic insult and decreased between 24 and 168 h. The lesion at 168 h was significantly larger than that following 1 h of ischemia and similar to that obtained at 4 h, suggesting that the maximum extent of tissue damage (without the involvement of significant edema) was reached within the first 4 h in this model. The enlargement of the lesion after 4 h correlated closely with changes in brain water content.

Protective effect of the glutamate antagonist, MK-801 in focal cerebral ischemia in the cat

The effects of the glutamate N-methyl-D aspartate (NMDA) receptor antagonist, MK-801, upon ischemic brain damage has been examined in anesthetized cats. Focal cerebral ischemia was produced by permanent occlusion of one middle cerebral artery and the animal were killed 6 h later. The amount of early ischemic damage was assessed in coronal sections at 16 predetermined stereotactic planes. Pretreatment with MK-801 (5 mg/kg, i.v.), 30 min before occlusion of the middle cerebral artery significantly reduced the volume of ischemic damage (from 32.7 +/- 4.0% of the cerebral hemisphere in vehicle-treated cats to 16.2 +/- 4.5% in MK-801-treated cats). NMDA receptor antagonists that penetrate the blood-brain barrier, such as MK-801, merit further study as protective agents against ischemic brain damage.

Intestinal ischemia: treatment by peritoneal lavage with oxygenated perfluorochemical

Though the delivery of elemental oxygen to tissues ravaged by anaerobic infection may be useful, little data exists that suggests that such therapy may benefit ischemic tissue. We report the development of a model to test the question that peritoneal lavage with an oxygen containing solution may favorably influence occlusive intestinal ischemia. Adult Sprague-Dawley rats with Nembutal (sodium pentobarbital) anesthesia underwent midline laparotomy; a microvascular clamp was applied to the superior mesenteric artery (SMA); and an inflow and outflow lavage catheter was placed. Treatment groups included control rats undergoing SMA occlusion only without lavage, rats lavaged with albumin during SMA occlusion (medium control), and rats lavaged during SMA occlusion with oxygenated perfluorochemical FC-47 emulsified in albumin (O2-FC-47). The increase in serum L-lactate following occlusion was used as an index of intestinal injury whether the perfusate was maintained at room temperature (28 degrees C) or body temperature (37 degrees C). Beginning with time O, which corresponded to the time of unclamping, subsequent samples were collected at 15, 30, and 60 minutes after a 30-minute SMA occlusion. Sequential lactates in 13 control rats were 4.18, 4.10, 3.88, and 4.52 mmol/L. Albumin lavaged animals had values at 28 degrees C of 2.23, 1.35, 1.8, and 2.44 mmol/L and values at 37 degrees C of 2.22, 1.40, 2.07, and 3.21 mmol/L, respectively. With O2-FC-47 lavage the respective lactates were 1.89, 1.09, 1.32, and 1.44 mmol/L at 28 degrees C and 2.14, 2.19, 2.50, and 2.1 mmol/L at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Perfluorocarbon blood substitutes

The salient physicochemical properties of the fluorocarbons are briefly reviewed, including their solubility for the physiologically important gases and their properties relevant to formulation (nonmiscibility with water). The preparations used to date are described, including their properties and compositions, with some comment about the available knowledge of the properties of the constituents. A critical review of the biological aspects and the possible uses of fluorocarbon emulsions constitutes the main body of the manuscript. Gas-transporting capabilities are considered quantitatively. The biological effects of these preparations are reviewed in in vivo, whole body systems, with some in vitro evidence where appropriate. The usefulness of these preparations investigated to date are reviewed under the broad headings of cardiovascular system, radiology, intoxications, and organ preservation. Finally, the shortcomings and potential usefulness are discussed, with recommendations for potential modifications.

Therapeutic progress--review XXIII. Are we making progress in the treatment of acute stroke?

The principal purpose of the treatment of acute stroke is to ensure that the quality of life of those affected is returned to as near normal as possible. Early nursing and physiotherapy are important components of effective management of acute stroke. It is not the intention of this review to examine these aspects which are so well described elsewhere (1). Instead, the theoretical and clinical bases for the various specific treatments advocated in recent years to reduce brain damage after ischaemic insult will be considered to serve as a guide for clinicians. Areas in this field where further research may prove rewarding are highlighted.