Clearance of brain edema and macromolecules through the cortical extracellular space

Interstitial fluid flow along white matter tracts: a potentially important mechanism for the dissemination of primary brain tumors

High grade astrocytomas remain incurable even though these tumors often appear localized on modern imaging studies, rarely metastasize to systemic sites, and can be aggressively treated with surgery and radiation therapy. Recent data suggest that the dissemination of astrocytoma cells along white matter tracts to distant regions of the brain may be responsible for the poor survival of these patients and the limited impact of local therapies. Movement of astrocytoma cells along these white matter tracts can be active or passive in nature. To study the potential for tumor dissemination by bulk flow of interstitial fluid resulting from peritumoral edema. 20 microL of tritiated inulin, Evans Blue, and rat albumin were injected stereotactically into the right frontal lobe and the left temporal lobe at the gray-white matter junction in Sprague-Dawley rats. Six hours later, the rats were sacrificed and the brains were removed, frozen and prepared for quantitative autoradiography and histologic analysis. Interstitial flow rates were calculated from the autoradiographs, and flow pathways were determined from the movement of Evans Blue, inulin and histologic data. In each animal injected in the frontal lobe, Evans Blue and inulin were primarily confined to large ipsilateral white matter tracts and extended from the frontal injection site to the occipital lobe. The average interstitial fluid flow rate in the association fibers of the external capsule was 0.86 mm/hr. In contrast, the animals receiving temporal lobe injections had Evans Blue and inulin confined to the temporal lobe. The average interstitial fluid flow rate in the white matter tracts of the temporal lobe was 0.61 mm/hr. The rapid and preferential flow of interstitial fluid along white matter tracts and the differences in the clearance of extracellular fluid observed between the frontal and temporal lobes may have important clinical implications. These data suggest that aggressive treatment of peritumoral edema, expansion of radiotherapy ports, and consideration of the location of the tumor in treatment planning may improve therapeutic outcomes for some patients. An improved understanding of the mechanisms of tumor dissemination is crucial to designing more effective therapeutic approaches for patients with this devastating malignancy.

The effect of intraventricular albumin in experimental brain oedema

Therapy for vasogenic brain oedema (VBE) is still an unsolved problem. Experimental work with the aim of establishing an oncotherapeutic option is presented. VBE is performed by focal freeze injury in rats. Using a stereotactic head holder hypo- or hyperosmolar human serum albumin is administered via the intraventricular route. The goal is to enhance the migration of oedema fluid with the aid of oncotic pressures. Early and late results are obtained for each group respectively four and twenty-four hours after the infliction of cold injury. The efficacy of therapy is evaluated by cerebrospinal fluid (CSF) osmolality, cerebral water content, tissue specific gravity, and blood-brain barrier (BBB) permeability. Posttherapeutic values for CSF osmolality are obtained by cisterna magna puncture. Hyperosmolar CSF after performance of cold injury (p < 0.05) is thought to be a result of fluid accumulation in the traumatized region partially from the intraventricular space. Posttherapeutic values after hyperosmolar albumin administration have revealed iso-osmolar CSF, increase in specific gravity (p < 0.001), and decrease in BBB permeability (p < 0.05). These results are in accordance with withdrawal of oedema fluid into the ventricles which can be interpreted as a positive therapeutic effect. Late results in hyperosmolar group have disclosed a hypo-iso-osmolar CSF, persistent increase in specific gravity, and no regression. These values have shown that hyperosmolar albumin administration does not interfere with CSF circulation. Early results of hypoosmolar albumin application are discouraging. This preliminary work of a therapeutic trial on VBE may be a basis for future investigations with different dosages and time modalities.

Characterization of edema by diffusion-weighted imaging in experimental traumatic brain injury

The objective of this study was to use diffusion-weighted magnetic resonance imaging (DWI) to help detect the type of edema that develops after experimental trauma and trauma coupled with hypotension and hypoxia (THH). Reduction in the apparent diffusion coefficients (ADCs) is thought to represent cytotoxic edema. In a preliminary series of experiments, the infusion edema model and middle cerebral artery occlusion models were used to confirm the direction of ADC change in response to purely extracellular and cytotoxic edema, respectively. The ADCs increased (p<0.05) in the case of extracellular edema and decreased (p<0.001) in cytotoxic edema. Following these initial experiments, a new impact acceleration model was used to induce traumatic brain injury. Thirty-six adult Sprague-Dawley rats were separated into four groups; sham, trauma alone, hypoxia and hypotension (HH), and THH. Following trauma, a 30-minute insult of hypoxia (PaO2 of 40 mm Hg) and hypotension (mean arterial blood pressure (MABP) of 30 mm Hg) were imposed and the animals were resuscitated. The DWI was carried out at four 1-hour intervals postinjury, and MABP, intracranial pressure (ICP), cerebral perfusion pressure (CPP), and cerebral blood flow (CBF) were monitored. The ADCs in the control and HH groups remained unchanged. The ADCs in the THH group rapidly decreased from a control level of 0.68 +/- 0.05 x 10(-3) mm2/second to 0.37 +/- 0.09 x 10(-3) mm2/second by 3 hours posttrauma (p < 0.001). In this group, the decreased CBF and CPP during secondary insult remained low despite resuscitation, with the ICP increasing to 56 +/- 7 mm Hg by 3 hours. In the trauma alone group, the rise in ICP reached a maximum value (28 +/- 3 mm Hg) at 30 minutes with a significant and sustained increase in CBF despite a gradual decrease in CPP. The ADCs in this group were not significantly reduced. The data lead the authors to suggest that the rise in ICP following severe trauma coupled with secondary insult in this model is predominately caused by cytotoxic edema and that ischemia plays a major role in the development of brain edema after head injury.

Doxorubicin encapsulated in sterically stabilized liposomes for the treatment of a brain tumor model: biodistribution and therapeutic efficacy

Anthracyclines entrapped in small-sized, sterically stabilized liposomes have the advantage of long circulation time, reduced systemic toxicity, increased uptake into systemic tumors, and gradual release of their payload. To date, there is no information on the behavior of these liposomes in brain tumors. The objective of this study was to compare the biodistribution and clinical efficacy of free doxorubicin (F-DOX) and stealth liposome-encapsulated DOX (SL-DOX) in a secondary brain tumor model. Nine days after tumor inoculation Fischer rats with a right parietal malignant sarcoma received an intravenous dose of 6 mg/kg of either F-DOX or SL-DOX for evaluation of drug biodistribution. For therapeutic trials a single dose of 8 mg/kg was given 6 or 11 days after tumor induction, or alternatively, weekly doses (5 mg/kg) were given on Days 6, 13, and 20. Liposome-encapsulated DOX was slowly cleared from plasma with a t1/2 of 35 hours. Free-DOX maximum tumor drug levels reached a mean value of 0.8 microgram/g and were identical in the adjacent brain and contralateral hemisphere. In contrast, SL-DOX tumor levels were 14-fold higher at their peak levels at 48 hours, declining to ninefold increased levels at 120 hours. A gradual increase in drug levels in the brain adjacent to tumor was noted between 72 and 120 hours (up to 4 micrograms/g). High-performance liquid chromatography analysis identified a small amount of aglycone metabolites within the tumor mass from 96 hours and beyond, after SL-DOX injection. Cerebrospinal fluid levels were barely detectable in tumor-bearing rats treated with F-DOX up to 120 hours after drug injection (< or = 0.05 microgram/ml), whereas the levels found after SL-DOX were 10- to 30-fold higher. An F-DOX single-dose treatment given 6 days after tumor inoculation increased the rats' life span (ILS) by 135% over controls (p < 0.05) but was not effective if given on Day 11. In contrast, SL-DOX treatment resulted in an ILS of 168% (p < 0.0003) with no difference when given after 6 or 11 days. Treatment with three weekly doses of SL-DOX produced an ILS of 189% compared to 126% by F-DOX (p < 0.0002). The authors conclude that the use of long-circulating liposomes as cytotoxic drug carriers in brain tumor results in enhanced drug exposure and improved therapeutic activity, with equal effectiveness against early small- and large-sized brain tumors.

Convection-enhanced distribution of large molecules in gray matter during interstitial drug infusion

Many novel experimental therapeutic agents, such as neurotrophic factors, enzymes, biological modifiers, and genetic vectors, do not readily cross the blood-brain barrier. An effective strategy to deliver these compounds to the central nervous system is required for their application in vivo. Under normal physiological conditions, brain interstitial fluid moves by both bulk flow (convection) and diffusion. It has recently been shown that interstitial infusion into the white matter can be used to increase bulk flow, produce interstitial convection, and efficiently and homogeneously deliver drugs to large regions of brain without significant functional or structural damage. In theory, even more uniform distribution is likely in gray matter. In the current study, four experiments were performed to examine if convection-enhanced delivery could be used to achieve regional distribution of large molecules in gray matter. First, the volume and consistency of anatomical distribution of 20 microliters of phaseolus vulgaris-leukoagglutinin (PHA-L; molecular weight (MW) 126 kD) after continuous high-flow microinfusion into the striatum of five rats over 200 minutes were determined using immunocytochemistry and quantified with image analysis. Second, the concentration profile of 14C-albumin (MW 69 kD) infused under identical conditions was determined in four hemispheres using quantitative autoradiography. Third, the volume of distribution after convection-enhanced infusion of 250 or 500 microliters biotinylated dextran (b-dextran, MW 10 kD), delivered over 310 minutes into the caudate and putamen of a rhesus monkey from one (250 microliters) or two (500 microliters) cannulas, was determined using immunocytochemistry and quantified with image analysis. Finally, the ability to target all dopaminergic neurons of the nigrostriatal tract via perfusion of the striatum with subsequent retrograde transport was assessed in three experiments by immunohistochemical analysis of the mesencephalon following a 300-minute infusion of 27 microliters horseradish peroxidase-labeled wheat germ agglutinin (WGA-HRP) into the striatum. Convection-enhanced delivery reproducibly distributed the large-compound PHA-L throughout the rat striatum (the percent volume of the striatum perfused, Vs, was 86% +/- 5%; mean +/- standard deviation) and produced a homogeneous tissue concentration in the perfused region (concentration of 14C-albumin relative to infusate concentration 30% +/- 5%). In the monkey, the infusion widely distributed b-dextran within the striatum using one cannula (caudate and putamen Vs = 76% and 76%) or two cannulas (Vs = 90% and 71%).(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of extravasated serum protein after cryoinjury in neonatal and adult rat brains

The sequelae of cryoinjury to unilateral cerebral cortex were compared in neonatal and adult rats. In neonatal rats, immunostaining for autologous albumin disclosed a wide spread of extravasated albumin in both hemispheres on day 1 and rapid clearance from the tissue by day 7, whereas in adults rats, the distribution of albumin had progressively increased by day 7 and was then restricted to the injury site by day 14. Horseradish peroxidase tracing revealed a leakage of serum proteins by day 3 in neonates and by day 7 in adults. The rapid clearance of serum proteins from the neonatal brain tissue appeared to be promoted by vimentin-positive radial glia in the subpial and periventricular regions. A possible causal relationship between the rapid clearance of serum proteins and unique outcome of the cryoinjury in the neonatal brain is discussed.

Convection-enhanced delivery of macromolecules in the brain

For many compounds (neurotrophic factors, antibodies, growth factors, genetic vectors, enzymes) slow diffusion in the brain severely limits drug distribution and effect after direct drug administration into brain parenchyma. We investigated convection as a means to enhance the distribution of the large and small molecules 111In-labeled transferrin (111In-Tf; M(r), 80,000) and [14C]sucrose (M(r), 359) over centimeter distances by maintaining a pressure gradient during interstitial infusion into white matter to generate bulk flow through the brain interstitium. The volume of distribution (Vd) containing > or = 1% concentration of infusion solution increased linearly with the infusion volume (Vi) for 111In-Tf(Vd/Vi, 6:1) and [14C]sucrose (Vd/Vi, 13:1). Twenty-four hours after infusion, the distribution of 111In-Tf was increased and more homogeneous, and penetration into gray matter had occurred. By using convection to supplement simple diffusion, enhanced distribution of large and small molecules can be obtained in the brain while achieving drug concentrations orders of magnitude greater than systemic levels.

Transdural cortical stabbing facilitates the drainage of edema fluid out of cold-injured brain

Recent experimental results indicate that cerebral glia lining and glia limitans may be barriers for plasma protein extravasated from injured cerebral microvessels flowing into the adjacent subarachnoid space. Therefore, it has been hypothesized that a transdural cortical stabbing which opens both the pia lining and glia limitans may facilitate drainage of edema fluid into the subarachnoid space and minimize brain edema. This hypothesis was tested in Sprague-Dawley rats with a transdural cold-injury on the right parietal cortex. The animals were sacrificed 24 hours later. One hour before being sacrificed 0.6 ml of 2% Evans blue was intravenously injected to determining the Evans blue distribution area. For measuring the inulin retention volume in the brain, 14C-inulin (10 microCi) in 1 ml of saline was injected intravenously at 10 min before sacrifice. The extent of brain edema was assessed by measuring the water content, the inulin retention volume, and the distribution area of Evans blue in the brain. Our results showed that the transdural cortical stabbing did not alter the water content of the cerebral hemisphere with cold lesion. However, it did effectively diminish the inulin retention volume by 26% as well as the distribution area of Evans blue by 22% in the cerebral hemisphere with cold lesion. In conclusion, a transdural cortical stabbing on the injured cortex may be beneficial for vasogenic brain edema.

Traumatic brain edema: an overview

This article provides a brief summary of concepts describing the formation and resolution of traumatic brain edema. Recent laboratory and clinical data are reviewed targeted toward resolving the contribution of edema to the swelling process. These data, indicate that blood volume is reduced in areas of ischemia following traumatic injury and edema volume is increased. Thus, edema is the major contributor to the swelling process in diffuse injury. As clinical MRI studies have not revealed barrier compromise in the presence of swelling, it is considered that other forms of edema, primarily ischemic and neurotoxic, make a substantial contribution to the edema volume.