Blood-brain barrier tight junctions are altered during a 72-h exposure to lambda-carrageenan-induced inflammatory pain

Neuron-glial interactions in blood-brain barrier formation

The blood brain barrier (BBB) evolved to preserve the microenvironment of the highly excitable neuronal cells to allow for action potential generation and propagation. Intricate molecular interactions between two main cell types, the neurons and the glial cells, form the underlying basis of the critical functioning of the nervous system across species. In invertebrates, interactions between neurons and glial cells are central in establishing a functional BBB. However, in vertebrates, the BBB formation and function is coordinated by interactions between neurons, glial cells, and endothelial cells. Here we review the neuron-glial interaction-based blood barriers in invertebrates and vertebrates and provide an evolutionary perspective as to how a glial-barrier system in invertebrates evolved into an endothelial barrier system. We also summarize the clinical relevance of the BBB as this protective barrier becomes disadvantageous in the pharmacological treatment of various neurological disorders.

Decreased blood-brain barrier permeability to fluorescein in streptozotocin-treated rats

Investigations of the blood-brain barrier (BBB) in diabetes have yielded contradictory results. It is possible that diabetes differentially affects paracellular and transcellular permeabilities via modulation of tight junction and transport proteins, respectively. Fluorescein (FL), a marker for paracellular permeability, is a substrate for the transport proteins organic anion transporter (OAT)-3 and multidrug resistance protein (MRP)-2 at the BBB. Furthermore, MRP-2-mediated efflux of FL can be upregulated by glucose. In this study, streptozotocin-induced diabetes led to decreased brain distribution of FL measured by in situ brain perfusion, consistent with activation of an efflux transport system for FL at the BBB. This change was paralleled by increased protein expression of MRP-2, but not OAT-3, in cerebral microvessels. These data indicate that diabetes may lead to changes in efflux transporters at the BBB and have implications for delivery of therapeutics to the central nervous system.

Increased blood-brain barrier permeability and altered tight junctions in experimental diabetes in the rat: contribution of hyperglycaemia and matrix metalloproteinases

AIMS/HYPOTHESIS

Although diabetes mellitus is associated with peripheral microvascular complications and increased risk of neurological events, the mechanisms by which diabetes disrupts the blood-brain barrier (BBB) are not known. Matrix metalloproteinase (MMP) activity is increased in diabetic patients, is associated with degradation of tight junction proteins, and is a known mediator of BBB compromise. We hypothesise that diabetes leads to compromise of BBB tight junctions via stimulation of MMP activity.

MATERIALS AND METHODS

Diabetes was induced in the rat with streptozotocin. At 14 days after injection, BBB function was assessed by in situ brain perfusion. Tight junction proteins were assessed by immunoblot and immunofluorescence. Plasma MMP activity was quantified by fluorometric gelatinase assay and gel zymography.

RESULTS

In streptozotocin-treated animals, permeability to [(14)C]sucrose increased concurrently with decreased production of BBB tight junction proteins occludin (also known as OCLN) and zona occludens 1 (ZO-1, also known as tight junction protein 1 or TJP1). Insulin treatment, begun on day 7, normalised blood glucose levels and attenuated BBB hyperpermeability to [(14)C]sucrose. Neither acute hyperglycaemia in naive animals nor acute normalisation of blood glucose in streptozotocin-treated animals altered BBB permeability to [(14)C]sucrose. Plasma MMP activity was increased in streptozotocin-treated animals.

CONCLUSIONS/INTERPRETATION

These data indicate that diabetes increases BBB permeability via a loss of tight junction proteins, and that increased BBB permeability in diabetes does not result from hyperglycaemia alone. Increased plasma MMP activity is implicated in degradation of BBB tight junction proteins and increased BBB permeability in diabetes. Peripheral MMP activity may present a novel target for protection of the BBB and prevention of neurological complications in diabetes.

Pathophysiology of the blood-brain barrier: animal models and methods

The specialized cerebral microvascular endothelium interacts with the cellular milieu of the brain and extracellular matrix to form a neurovascular unit, one aspect of which is a regulated interface between the blood and central nervous system (CNS). The concept of this blood-brain barrier (BBB) as a dynamically regulated system rather than a static barrier has wide-ranging implications for pathophysiology of the CNS. While in vitro models of the BBB are useful for screening drugs targeted to the CNS and indispensable for studies of cerebral endothelial cell biology, the complex interactions of the neurovascular unit make animal-based models and methods essential tools for understanding the pathophysiology of the BBB. BBB dysfunction is a complication of neurodegenerative disease and brain injury. Studies on animal models have shown that diseases of the periphery, such as diabetes and inflammatory pain, have deleterious effects on the BBB which may contribute to neurological complications associated with these conditions. Furthermore, genetic and/or epigenetic abnormalities in constituents of the BBB may be significant contributing factors in disease etiology. Research that approaches the BBB as a dynamic system integrated with both the CNS and the periphery is therefore critical to understanding and treating diseases of the CNS. Herein, we review various methodological approaches used to study BBB function in the context of disease. These include measurement of transport between blood and brain, imaging-based technologies, and genomic/proteomic approaches.

Biphasic cytoarchitecture and functional changes in the BBB induced by chronic inflammatory pain

The blood-brain barrier (BBB) is a dynamic system which maintains brain homeostasis and limits CNS penetration via interactions of transmembrane and intracellular proteins. Inflammatory pain (IP) is a condition underlying several diseases with known BBB perturbations, including stroke, Parkinson's, multiple sclerosis and Alzheimer's. Exploring the underlying pathology of chronic IP, we demonstrated alterations in BBB paracellular permeability with correlating changes in tight junction (TJ) proteins: occludin and claudin-5. The present study examines the IP-induced molecular changes leading to a loss in functional BBB integrity. IP was induced by injection of Complete Freund's Adjuvant (CFA) into the plantar surface of the right hindpaw of female Sprague-Dawley rats. Inflammation and hyperalgesia were confirmed, and BBB paracellular permeability was assessed by in situ brain perfusion of [14C]sucrose (paracellular diffusion marker). The permeability of the BBB was significantly increased at 24 and 72 h post-CFA. Analysis of the TJ proteins, which control the paracellular pathway, demonstrated decreased claudin-5 expression at 24 h, and an increase at 48 and 72 h post-injection. Occludin expression was significantly decreased 72 h post-CFA. Expression of junction adhesion molecule-1 (JAM-1) increased 48 h and decreased by 72 h post-CFA. Confocal microscopy demonstrated continuous expression of both occludin and JAM-1, each co-localizing with ZO-1. The increased claudin-5 expression was not limited to the junction. These results provide evidence that chronic IP causes dramatic alterations in specific cytoarchitectural proteins and demonstrate alterations in molecular properties during CFA, resulting in significant changes in BBB paracellular permeability.

Diapedesis of monocytes is associated with MMP-mediated occludin disappearance in brain endothelial cells

The blood-brain barrier (BBB), a selective barrier formed by endothelial cells and dependent on the presence of tight junctions, is compromised during neuroinflammation. A detailed study of tight junction dynamics during transendothelial migration of leukocytes has been lacking. Therefore, we retrovirally expressed green fluorescent protein (GFP) fused to the N-terminus of the tight junction protein occludin in the rat brain endothelial cell line GP8/3.9. Confocal microscopy analyses revealed that GFP-occludin colocalized with the intracellular tight junction protein, ZO-1, localized at intercellular connections, and was absent at cell borders lacking apposing cells. Using live cell imaging we found that monocytes scroll over the brain endothelial cell surface toward cell-cell contacts, induce gap formation, which is associated with local disappearance of GFP-occludin, and subsequently traverse the endothelium paracellularly. Immunoblot analyses indicated that loss of occludin was due to protein degradation. The broad spectrum matrix metalloproteinase (MMP) inhibitor BB-3103 significantly inhibited endothelial gap formation, occludin loss, and the ability of monocytes to pass the endothelium. Our results provide a novel insight into the mechanism by which leukocytes traverse the BBB and illustrate that therapeutics aimed at the stabilization of the tight junction may be beneficial to resist a neuroinflammatory attack.

Streptozotocin-induced diabetes progressively increases blood-brain barrier permeability in specific brain regions in rats

This study investigated the effects of streptozotocin-induced diabetes on the functional integrity of the blood-brain barrier in the rat at 7, 28, 56, and 90 days, using vascular space markers ranging in size from 342 to 65,000 Da. We also examined the effect of insulin treatment of diabetes on the formation and progression of cerebral microvascular damage and determined whether observed functional changes occurred globally throughout the brain or within specific brain regions. Results demonstrate that streptozotocin-induced diabetes produced a progressive increase in blood-brain barrier permeability to small molecules from 28 to 90 days and these changes in blood-brain barrier permeability were region specific, with the midbrain most susceptible to diabetes-induced microvascular damage. In addition, results showed that insulin treatment of diabetes attenuated blood-brain barrier disruption, especially during the first few weeks; however, as diabetes progressed, it was evident that microvascular damage occurred even when hyperglycemia was controlled. Overall, results of this study suggest that diabetes-induced perturbations to cerebral microvessels may disrupt homeostasis and contribute to long-term cognitive and functional deficits of the central nervous system.

Age-related changes in neuroprotection: is estrogen pro-inflammatory for the reproductive senescent brain?

Estrogen replacement therapy (ERT) is widely prescribed to postmenopausal women for relief from the adverse vasomotor effects of menopause, to reduce bone loss, to improve cardiovascular health, and to protect against metabolic disorders. However, there is now greater awareness of the increased risk to benefit ratio from the recently concluded Women's Health Initiative Memory Study (WHIMS), which reported that ERT increased the risk of cognitive impairment and dementia in elderly women. Studies from the experimental literature indicate that while estrogen is neuroprotective in many instances, estrogen replacement can be deleterious in some cases. These differences may be partly due to the age and species of the experimental model. The majority of the experimental data comes from studies where the age or endocrine status of the animal model is not comparable to that of menopausal or postmenopausal women, such as those in the WHIMS study. In this review, we will focus on age-related changes in estrogen's neuroprotective effects and evidence that reproductive senescence-related changes in the blood-brain barrier and the immune system may result in deleterious consequences for ERT.

Assessment of a bioactive compound for its potential antiinflammatory property by tight junction permeability

Lactobacillus probiotic strains are proving to be abundant sources of bioactive components, including antiinflammatory components. Lifree was made of fruits fermented by Lactobacillus paracasei, Lactobacillus reuterrii and Saccharomyces cerevisiae. This study was designed to test these compounds in cell assays measuring epithelial barrier function and proliferation in the first instance. Cell proliferation was measured in mouse fibroblasts cells (3T3NIH) and rat intestinal epithelial cells (IEC-6), and tight junction activity in the kidney epithelial cell line (MDCK). Tight junction permeability was assessed by measuring transepithelial electrical resistance (TER) across confluent monolayers, following the addition of Lifree with or without a challenge with EGTA. Lifree promoted tight junction formation and recovery following loss of TER from challenge with EGTA. On the other hand, Lifree did not stimulate cell growth in either 3T3NIH and IEC-6 cells. Lifree stimulates tight junction maintenance and formation, suggesting it may have potential antiinflammatory properties.

Expression of tight and gap junctional proteins in the perineurial window model of the rat sciatic nerve

Limited perineurial injury, known as a perineurial window, can lead to neuropathic pain. This article hypothesizes that the recovery of the perineurium is associated with the intercellular junctional proteins. It analyzes the expressions of occludin, ZO-1, and connexin 43 by immunoconfocal microscopy. Seven days after injury, immunoreactivities for occludin and ZO-1 were observed, although there was no connexin 43 detected. Then, 21 days after injury, immunoreactivity for connexin 43 were observed. These results indicate that recovery of the perineurium is associated with the intercellular junctional proteins and that the recovery of gap junctions is delayed compared with that of tight junctions.

Development of tight junction molecules in blood vessels of germinal matrix, cerebral cortex, and white matter

Tight junction (TJ) molecules confer cell-to-cell adhesion to endothelial cells and, thus, provide structural integrity to blood vessels. Therefore, decreased expression of these molecules may be a cause of germinal matrix (GM) fragility and their propensity to hemorrhage in premature infants. The objective of this study was to compare the expression of endothelial TJ molecules, including claudin-5, occludin, and junction adhesion molecules (JAM), among blood vessels of GM, cortex, and white matter for fetuses and premature infants of gestational age 16-40 wk, and to examine their maturational changes with advancing gestational age. We measured the expression of claudin-1, claudin-5, occludin, and JAM in GM, cortex, and white matter in postmortem brain samples. We performed immunohistochemical staining on brain sections and Western blot to quantify these molecules. We found that claudin-5, occludin, and JAM-1 were expressed as early as 16 wk in GM, cortex, and white matter. Claudin-1, JAM-2, and JAM-3 were not detected in the GM, cortex, and white matter. Claudin-5, occludin, and JAM-1 did not change significantly as a function of gestational age. There was no significant difference in the expression of these molecules in the vasculature of GM compared with cortex and white matter. Because the primary endothelial TJ molecules, including claudin-5, occludin, and JAM-1, are expressed as early as 16 wk in the blood brain barrier and since as they are not decreased in GM vasculature compared with cortex and white matter, they are unlikely to be responsible for GM fragility and vulnerability to hemorrhage in premature infants.

Alterations in blood-brain barrier ICAM-1 expression and brain microglial activation after lambda-carrageenan-induced inflammatory pain

Previous studies showed that peripheral inflammatory pain increased blood-brain barrier (BBB) permeability and altered tight junction protein expression and the delivery of opioid analgesics to the brain. What remains unknown is which pathways and mediators during peripheral inflammation affect BBB function and structure. The current study investigated effects of lambda-carrageenan-induced inflammatory pain (CIP) on BBB expression of ICAM-1. We also examined the systemic contribution of a number of proinflammatory cytokines and microglial activation in the brain to elucidate pathways involved in BBB disruption during CIP. We investigated ICAM-1 RNA and protein expression levels in isolated rat brain microvessels after CIP using RT-PCR and Western blot analyses, screened inflammatory cytokines during the time course of inflammation, assessed white blood cell counts, and probed for BBB and central nervous system stimulation and leukocyte transmigration using immunohistochemistry and flow cytometry. Results showed an early increase in ICAM-1 RNA and protein expression after CIP with no change in circulating levels of several proinflammatory cytokines. Changes in ICAM-1 protein expression were noted at 48 h. Immunohistochemistry showed that the induction of ICAM-1 was region specific with increased expression noted in the thalamus and frontal and parietal cortices, which directly correlated with increased expression of activated microglia. The findings of the present study were that CIP induces increased ICAM-1 mRNA and protein expression at the BBB and that systemic proinflammatory mediators play no apparent role in the early response (1-6 h); however, brain region-specific increases in microglial activation suggest a potential for a central-mediated response.

The blood-brain barrier/neurovascular unit in health and disease

The blood-brain barrier (BBB) is the regulated interface between the peripheral circulation and the central nervous system (CNS). Although originally observed by Paul Ehrlich in 1885, the nature of the BBB was debated well into the 20th century. The anatomical substrate of the BBB is the cerebral microvascular endothelium, which, together with astrocytes, pericytes, neurons, and the extracellular matrix, constitute a "neurovascular unit" that is essential for the health and function of the CNS. Tight junctions (TJ) between endothelial cells of the BBB restrict paracellular diffusion of water-soluble substances from blood to brain. The TJ is an intricate complex of transmembrane (junctional adhesion molecule-1, occludin, and claudins) and cytoplasmic (zonula occludens-1 and -2, cingulin, AF-6, and 7H6) proteins linked to the actin cytoskeleton. The expression and subcellular localization of TJ proteins are modulated by several intrinsic signaling pathways, including those involving calcium, phosphorylation, and G-proteins. Disruption of BBB TJ by disease or drugs can lead to impaired BBB function and thus compromise the CNS. Therefore, understanding how BBB TJ might be affected by various factors holds significant promise for the prevention and treatment of neurological diseases.

Disruption of the blood-brain barrier during TNBS colitis

Well-documented central nervous system changes during colitis suggest possible alterations of blood-brain barrier (BBB) permeability, yet the integrity of the BBB has not been fully evaluated in experimental colitis. Our aim was to investigate whether trinitrobenzene sulphonic acid (TNBS) colitis was associated with an increase in the permeability of the BBB. Sprague-Dawley rats were given an intracolonic injection of saline or TNBS and studied 1, 2, 3, 7 and 21 days after treatment. The extravasation of endogenous immunoglobulin G, a large molecule, was not altered at any time after TNBS treatment. In contrast, significant increases in the BBB leakage of sodium fluorescein, a much smaller molecule, were observed 1 and 2 days after the induction of colitis, in and around the circumventricular organs; the organum vasculosum of the lamina terminalis, subfornical organ and median eminence of the hypothalamus. TNBS-treated rats also exhibited sodium fluorescein leakage in focal areas in the brain parenchyma. The expression of endothelial barrier antigen, a protein associated with the BBB, was reduced about 60% 48 h after the induction of colitis. This returned to control values by 3 weeks, when colitis had largely subsided. In conclusion, experimental colitis transiently increased permeability of the brain to small molecules through a mild disruption of the BBB.

Chronic inflammatory pain leads to increased blood-brain barrier permeability and tight junction protein alterations

The blood-brain barrier (BBB) maintains brain homeostasis by limiting entry of substances to the central nervous system through interaction of transmembrane and intracellular proteins that make up endothelial cell tight junctions (TJs). Recently it was shown that the BBB can be modulated by disease pathologies including inflammatory pain. This study examined the effects of chronic inflammatory pain on the functional and molecular integrity of the BBB. Inflammatory pain was induced by injection of complete Freund's adjuvant (CFA) into the right plantar hindpaw in female Sprague-Dawley rats under halothane anesthesia; control animals were injected with saline. Edema and hyperalgesia were assessed by plethysmography and infrared paw-withdrawal latency. At 72 h postinjection, significant edema formation and hyperalgesia were noted in the CFA-treated rats. Examination of permeability of the BBB by in situ perfusion of [14C]sucrose while rats were under pentobarbital anesthesia demonstrated that CFA treatment significantly increased brain sucrose uptake. Western blot analysis of BBB TJ proteins showed no change in expression of zonula occludens-1 (an accessory protein) or actin (a cytoskeletal protein) with CFA treatment. Expression of the transmembrane TJ proteins occludin and claudin-3 and -5 significantly changed with CFA treatment with a 60% decrease in occludin, a 450% increase in claudin-3, and a 615% increase in claudin-5 expression. This study demonstrates that during chronic inflammatory pain, alterations in BBB function are associated with changes in specific transmembrane TJ proteins.

Tolerance develops to the effect of lipopolysaccharides on movement-evoked hyperalgesia when administered chronically by a systemic but not an intrathecal route

Single exposures to lipopolysaccharides (LPS) produce deep tissue pain in humans and cutaneous hyperalgesia in rodents. While tolerance develops to many effects of LPS, sensitization to hyperalgesia is documented after a single injection. To determine the effect of long-term exposure to LPS, we explored the chronic effect of LPS on movement-evoked pain using a new assay based on grip force in mice. We found that a single systemic injection of LPS (i.p. or s.c.) induced a dose-related decrease in forelimb grip force responses beginning 6-8 h after injection and peaking between 9 and 24 h. The consequence of LPS is likely hyperalgesia rather than weakness as these decreases were rapidly attenuated by either 10 mg/kg of morphine i.p. or 10 microg of morphine injected intrathecally (i.t.). Complete tolerance to this hyperalgesia developed after repeated injections of LPS at doses of 0.9 mg/kg i.p. or 5 mg/kg s.c. Tolerance began after a single injection and was fully developed after as few as four injections of 5 mg/kg of LPS delivered s.c. The concentration of circulating LPS 5 h after a single parenteral injection was less in LPS-tolerant mice than naïve controls, suggesting that tolerance may result from a more efficient clearance of LPS from the circulation. Injected i.t., LPS also induced hyperalgesia, however, tolerance did not develop to multiple injections by this route. There was no cross-tolerance between s.c. and i.t. injections of LPS. These data indicate that decreases in grip force are a sensitive measure of LPS-induced movement-evoked hyperalgesia and that tolerance develops to parenteral but not central hyperalgesic effects of LPS.

Nicotine increases in vivo blood–brain barrier permeability and alters cerebral microvascular tight junction protein distribution

The blood-brain barrier (BBB) is critical to the health of the central nervous system. The BBB is formed primarily by the presence of tight junctions (TJ) between cerebral microvessel endothelial cells. In light of the known effects of nicotine on endothelial cell biology, the specific effects of nicotine on the in vivo BBB were examined. Using in situ brain perfusion, it was found that continuous administration of nicotine (4.5 mg free base x kg(-1) x day(-1)) for 1 and 7 days led to increased permeability of the BBB to [14C]-sucrose without significant changes in its initial volume of distribution. The expression and distribution of the TJ-associated proteins actin, occludin, claudin-1, -3, and -5, and ZO-1 and -2 were analyzed by Western blot and immunofluorescence microscopy. Though no changes in total protein expression were observed, nicotine treatment was associated with altered cellular distribution of ZO-1 and diminished junctional immunoreactivity of claudin-3. It is proposed that nicotine leads to changes in BBB permeability via the modulation of TJ proteins.

Mechanisms involved in the blood–brain barrier increased permeability induced by Phoneutria nigriventer spider venom in rats

We have recently demonstrated by electron microscopy, using lanthanum nitrate as an extracellular tracer, that the intravenous injection of Phoneutria nigriventer spider venom (PNV) induces blood-brain barrier (BBB) breakdown in rat hippocampus. One and nine days after PNV injection, tracer was found in pinocytic vesicles crossing the endothelium and in the interendothelial cleft, suggesting that BBB breakdown had occurred through enhanced transendothelial transport and/or tight-junction opening. In the present work, we investigated the mechanisms by which PNV (850 microg/kg, i.v.) increased the hippocampal microvascular permeability in rats 24 h after the endovenous administration. The expression and phosphorylation of some tight- and adherens junctions-associated proteins in hippocampal homogenate and hippocampal microvessel homogenate were assessed by Western blotting and immunoprecipitation. The microtubule-dependent transcellular transport was also evaluated by quantitative ultrastructural methods in pretreated rats with colchicine (0.5 mg/kg, i.p.), prior to PNV injection. Western blots showed no significant increase in the expression of the tight junction-associated proteins ZO-1 and occludin or in the adherens junction-associated beta-catenin after 24 h of PNV administration. Morphological study showed no alterations of the immunolabeling for occludin and ZO-1 in rat brain cryosection following PNV. In addition, no changes were observed in phosphotyrosine content of occludin and beta-catenin in PNV-treated rats compared with control animals. However, the disruption of microtubule-dependent transcellular transport by colchicine completely prevented (p<0.001) PNV-induced leakage of the BBB tracer. These findings indicate that the increased BBB permeability evoked by PNV in rats probably resulted from enhanced microtubule-dependent transendothelial vesicular transport, with no substantial involvement of the paracellular barrier in the time interval studied.

Monocyte chemoattractant protein-1 alters expression of tight junction-associated proteins in brain microvascular endothelial cells

The chemokine monocyte chemoattractant protein (MCP-1) is recognized to mediate extravasation of mononuclear leukocytes into the brain during a variety of neuroinflammatory conditions. In large part produced by parenchymal neural cells during these disease states, it is unclear how this chemokine can stimulate the migration of circulating leukocytes that lie behind the highly impermeant blood-brain barrier (BBB). Based on the premise that disruption of tight junctions (TJs) could foster leukocyte extravasation, experiments were conducted to test the hypothesis that MCP-1 alters the expression and/or distribution of the TJ-associated proteins zonulae occludens-1 (ZO-1) and occludin in brain microvascular endothelial cells (BMEC) comprising the BBB. Exposure to MCP-1 caused a loss in immunostaining of ZO-1 at inter-endothelial junctional regions in both cultured BMEC and isolated brain microvessels, as well as a similar effect on occludin in cultured BMEC, but did not alter occludin staining in microvessels. In cellular fractionation experiments, ZO-1 associated predominantly with the detergent-resistant cytoskeletal framework (CSK) in both cultured BMEC and brain microvessels, while a slimmer majority of occludin partitioned with the CSK. Following MCP-1 exposure, ZO-1 was reduced in the CSK fraction of cultured BMEC and microvessels, with a shift of ZO-1 to the detergent-soluble fraction in both cases. Occludin exhibited a similar pattern of MCP-1-induced loss and shift from the CSK in cultured BMEC, but remained nearly constant in microvessels. Lastly, expression of caveolin-1, a major structural component of membrane microdomains thought to be functionally complexed with TJs, was additionally altered by MCP-1 treatment of both cultured BMEC and microvessels. These results indicate that, in addition to its chemotactic activity, MCP-1 might alter BBB integrity during CNS inflammation.

Mannitol opening of the blood-brain barrier: regional variation in the permeability of sucrose, but not 86Rb+ or albumin

Clinically, infusion of hyperosmolar solutions is used to enhance chemotherapeutic drug penetration of the blood-brain barrier (BBB) in patients with malignant brain tumors or metastases. We examined the effect of hyperosmolar BBB disruption on brain permeability of three compounds, 86Rb+, a marker for K+ permeability and transport, [14C]sucrose and Evans blue albumin, using a rat in situ perfusion model. 86Rb+ and [14C]sucrose had increased permeability 20 min after BBB disruption with 1.6 M mannitol. There was no change in Evans blue albumin permeability. Only [14C]sucrose showed regional variation in permeability after mannitol-induced BBB disruption, with the cortex and midbrain having higher sucrose permeability then either the cerebellum or brainstem. These data suggest that the clinical efficacy of hyperosmolar disruption therapy in conjunction with chemotherapeutic agents, of a similar molecular weight to sucrose, may be affected by the location of the tumor within the brain.

Effect of λ-carrageenan-induced inflammatory pain on brain uptake of codeine and antinociception

This study investigated the potential clinical implications of lambda-carrageenan-induced inflammatory pain on brain uptake of a commonly used analgesic, codeine, in relation to the fundamental properties of the blood-brain barrier (BBB) correlated to its antinociceptive profile over a 168-h time course. BBB uptake of [14C]sucrose (a membrane impermeant marker) and [3H]codeine were investigated using an in situ brain perfusion model in the rat. Results demonstrated a significantly increased brain uptake of [14C]sucrose at 1, 3, 6 and 48 h (139+/-9%, 166+/-19%, 138+/-13% and 146+/-7% compared with control, respectively) and [3H]codeine at 3 and 48 h (179+/-6% and 179+/-12% compared with control, respectively). Capillary depletion analyses ensured that increased radioisotope associated with the brain was due to increased uptake rather than trapping in the cerebral vasculature. Antinociception studies using a radiant-heat tail flick analgesia method demonstrated that lambda-carrageenan-induced inflammatory pain enhanced the in vivo antinociceptive profile of i.p.-administered codeine (7 mg/kg) at 3 and 48 h (144+/-11% and 155+/-9% compared with control, respectively). This study demonstrated that brain uptake and antinociception of codeine are increased during lambda-carrageenan-induced inflammatory pain, suggesting that the presence of inflammatory pain may be an important consideration in therapeutic drug dosing, potential adverse effects and/or neurotoxicity.

Pain and the blood-brain barrier: obstacles to drug delivery

Delivery of drugs across the blood-brain barrier has been shown to be altered during pathological states involving pain. Pain is a complex phenomenon involving immune and centrally mediated responses, as well as activation of the hypothalamic-pituitary-adrenal axis. Mediators released in response to pain have been shown to affect the structure and function of the blood-brain barrier in vitro and in vivo. These alterations in blood-brain barrier permeability and cytoarchitecture have implications in terms of drug delivery to the central nervous system, since pain and inflammation have the capacity to alter drug uptake and efflux across the blood-brain barrier. An understanding of how blood-brain barrier and central nervous system drug delivery mechanisms are altered during pathological conditions involving pain and/or inflammation is important in designing effective therapeutic regimens to treat disease.