Plasma albumin is a potent trigger of calcium signals and DNA synthesis in astrocytes

Blood-brain barrier dysfunction, TGFβ signaling, and astrocyte dysfunction in epilepsy

Brain insults, including traumatic and ischemic injuries, are frequently followed by acute seizures and delayed development of epilepsy. Dysfunction of the blood-brain barrier (BBB) is a hallmark of brain insults and is usually surrounding the core lesion. Recent studies from several laboratories confirmed that vascular pathology is involved in the development of epilepsy and demonstrate a key role for astroglia in this process. In this review, we focus on glia-related mechanisms linking vascular pathology, and specifically BBB dysfunction, to seizures and epilepsy. We summarize molecular and physiological experimental data demonstrating that the function of astrocytes is altered due to direct exposure to serum albumin, mediated by transforming growth factor beta signaling. We discuss the reported changes and their potential role in the observed hyperexcitability as well as potential implications of these findings for the future development of new diagnostic modalities and treatments to allow a full implementation of the gained knowledge for the benefit of patients with epilepsy.

Pathophysiology of the neurovascular unit: disease cause or consequence?

Pathophysiology of the neurovascular unit (NVU) is commonly seen in neurological diseases. The typical features of NVU pathophysiology include tissue hypoxia, inflammatory and angiogenic activation, as well as initiation of complex molecular interactions between cellular (brain endothelial cells, astroctyes, pericytes, inflammatory cells, and neurons) and acellular (basal lamina) components of the NVU, jointly resulting in increased blood-brain barrier permeability, brain edema, neurovascular uncoupling, and neuronal dysfunction and damage. The evidence of important role of the brain vascular compartment in disease pathogenesis has elicited the debate whether the primary vascular events may be a cause of the neurological disease, as opposed to a mere participant recruited by a primary neuronal origin of pathology? Whereas some hereditary and acquired cerebral angiopathies could be considered a primary cause of neurological symptoms of the disease, the epidemiological studies showing a high degree of comorbidity among vascular disease and dementias, including Alzheimer's disease, as well as migraine and epilepsy, suggested that primary vascular pathology may be etiological factor causing neuronal dysfunction or degeneration in these diseases. This review focuses on recent hypotheses and evidence, suggesting that pathophysiology of the NVU may be initiating trigger for neuronal pathology and subsequent neurological manifestations of the disease.

A novel in vitro human microglia model: characterization of human monocyte-derived microglia

Microglia are the innate immune cells of the central nervous system. They help maintaining physiological homeostasis and contribute significantly to inflammatory responses in the course of infection, injury and degenerative processes. To date, there is no standardized simple model available to investigate the biology of human microglia. The aim of this study was to establish a new human microglia model. For that purpose, human peripheral blood monocytes were cultured in serum free medium in the presence of M-CSF, GM-CSF, NGF and CCL2 to generate monocyte-derived microglia (M-MG). M-MG were clearly different in morphology, phenotype and function from freshly isolated monocytes, cultured monocytes in the absence of the cytokines and monocyte-derived dendritic cells (M-DC) cultured in the presence of GM-CSF and IL-4. M-MG acquired a ramified morphology with primary and secondary processes. M-MG displayed a comparable phenotype to the human microglia cell line HMC3, expressing very low levels of CD45, CD14 and HLA-DR, CD11b and CD11c; and undetectable levels of CD40, CD80 and CD83, and a distinct pattern of chemokine receptors (positive for CCR1, CCR2, CCR4, CCR5, CXCR1, CXCR3, CX3CR1; negative for CCR6 and CCR7). In comparison with M-DC, M-MG displayed lower T-lymphocyte stimulatory capacity, as well as lower phagocytosis activity. The described protocol for the generation of human monocyte-derived microglia is feasible, well standardized and reliable, as it uses well defined culture medium and recombinant cytokines, but no serum or conditioned medium. This protocol will certainly be very helpful for future studies investigating the biology and pathology of human microglia.

Medicinal chemistry based approaches and nanotechnology-based systems to improve CNS drug targeting and delivery

The central nervous system (CNS) is protected by various barriers, which regulate nervous tissue homeostasis and control the selective and specific uptake, efflux, and metabolism of endogenous and exogenous molecules. Among these barriers is the blood-brain barrier (BBB), a physical and physiological barrier that filters very efficiently and selectively the entry of compounds from the blood to the brain and protects nervous tissue from harmful substances and infectious agents present in the bloodstream. The BBB also prevents the entry of potential drugs. As a result, various drug targeting and delivery strategies are currently being developed to enhance the transport of drugs from the blood to the brain. Following a general introduction, we briefly overview in this review article the fundamental physiological properties of the BBB. Then, we describe current strategies to bypass the BBB (i.e., invasive methods, alternative approaches, and temporary opening) and to cross it (i.e., noninvasive approaches). This section is followed by a chapter addressing the chemical and technological solutions developed to cross the BBB. A special emphasis is given to prodrug-targeting approaches and targeted nanotechnology-based systems, two promising strategies for BBB targeting and delivery of drugs to the brain.

Minimally invasive molecular delivery into the brain using optical modulation of vascular permeability

Systemic delivery of bioactive molecules in the CNS is hampered by the blood-brain barrier, which has bottlenecked noninvasive physiological study of the brain and the development of CNS drugs. Here we report that irradiation with an ultrashort pulsed laser to the blood vessel wall induces transient leakage of blood plasma without compromising vascular integrity. By combining this method with a systemic injection, we delivered target molecules in various tissues, including the brain cortex. This tool allows minimally invasive local delivery of chemical probes, nanoparticles, and viral vectors into the brain cortex. Furthermore, we demonstrated astrocyte-mediated vasodilation in vivo without opening the skull, using this method to load a calcium indicator in conjunction with label-free photoactivation of astrocytes.

Reduction of neurovascular damage resulting from microelectrode insertion into the cerebral cortex using in vivo two-photon mapping

Penetrating neural probe technologies allow investigators to record electrical signals in the brain. The implantation of probes causes acute tissue damage, partially due to vasculature disruption during probe implantation. This trauma can cause abnormal electrophysiological responses and temporary increases in neurotransmitter levels, and perpetuate chronic immune responses. A significant challenge for investigators is to examine neurovascular features below the surface of the brain in vivo. The objective of this study was to investigate localized bleeding resulting from inserting microscale neural probes into the cortex using two-photon microscopy (TPM) and to explore an approach to minimize blood vessel disruption through insertion methods and probe design. 3D TPM images of cortical neurovasculature were obtained from mice and used to select preferred insertion positions for probe insertion to reduce neurovasculature damage. There was an 82.8 +/- 14.3% reduction in neurovascular damage for probes inserted in regions devoid of major (>5 microm) sub-surface vessels. Also, the deviation of surface vessels from the vector normal to the surface as a function of depth and vessel diameter was measured and characterized. 68% of the major vessels were found to deviate less than 49 microm from their surface origin up to a depth of 500 microm. Inserting probes more than 49 microm from major surface vessels can reduce the chances of severing major sub-surface neurovasculature without using TPM.

Bridging the Divide between Neuroprosthetic Design, Tissue Engineering and Neurobiology

Neuroprosthetic devices have made a major impact in the treatment of a variety of disorders such as paralysis and stroke. However, a major impediment in the advancement of this technology is the challenge of maintaining device performance during chronic implantation (months to years) due to complex intrinsic host responses such as gliosis or glial scarring. The objective of this review is to bring together research communities in neurobiology, tissue engineering, and neuroprosthetics to address the major obstacles encountered in the translation of neuroprosthetics technology into long-term clinical use. This article draws connections between specific challenges faced by current neuroprosthetics technology and recent advances in the areas of nerve tissue engineering and neurobiology. Within the context of the device-nervous system interface and central nervous system implants, areas of synergistic opportunity are discussed, including platforms to present cells with multiple cues, controlled delivery of bioactive factors, three-dimensional constructs and in vitro models of gliosis and brain injury, nerve regeneration strategies, and neural stem/progenitor cell biology. Finally, recent insights gained from the fields of developmental neurobiology and cancer biology are discussed as examples of exciting new biological knowledge that may provide fresh inspiration toward novel technologies to address the complexities associated with long-term neuroprosthetic device performance.

Albumin activates astrocytes and microglia through mitogen-activated protein kinase pathways

Following acute brain injury, albumin may gain access to the brain parenchyma. Clinical studies indicate a protective role for albumin in stroke but an increase in mortality associated with albumin administration following traumatic brain injury. We investigated the effects of albumin on astrocyte and microglial activation, and the role of mitogen-activated protein kinases (MAPK) in these responses. Albumin activated ERK1/2, p38 MAPK and JNK signaling pathways in astrocytes, and induced the production of interleukin (IL)-1beta, inducible nitric oxide (NO) synthase, the NO metabolite nitrite, and the chemokine CX3CL1 while reducing the level of S100B. The release of inflammatory markers by astrocytes was partially dependent on p38 MAPK and ERK1/2 pathways, but not JNK. In microglia, albumin exposure activated all three MAPK pathways and produced an increase in IL-1beta and nitrite. Inhibition of p38 MAPK in microglia leads to an increased level of IL1beta, while inhibition of all three MAPKs suppressed the release of nitrite. These results suggest that albumin activates astrocytes and microglia, inducing inflammatory responses involved both in the mechanisms of cellular injury and repair via activation of MAPK pathways, and thereby implicate glial activation in the clinical responses to administration of albumin.

Alzheimer's disease drug development and the problem of the blood-brain barrier

Alzheimer's disease (AD) drug development is limited by the presence of the blood-brain barrier (BBB). More than 98% of all small-molecule drugs, and approximately 100% of all large-molecule drugs, do not cross the BBB. Although the vast majority of AD drug candidates do not cross the BBB, the present-day AD drug-development effort is characterized by an imbalance wherein >99% of the drug-development effort is devoted to central nervous system (CNS) drug discovery, and <1% of drug development is devoted to CNS drug delivery. Future AD drug development needs a concerted effort to incorporate BBB sciences early in the CNS drug discovery process. This goal can be achieved by a reallocation of resources, and an expansion of research efforts in the pure science of BBB biology and the applied science of brain drug-targeting technology.

Structure and function of the blood-brain barrier

Neural signalling within the central nervous system (CNS) requires a highly controlled microenvironment. Cells at three key interfaces form barriers between the blood and the CNS: the blood-brain barrier (BBB), blood-CSF barrier and the arachnoid barrier. The BBB at the level of brain microvessel endothelium is the major site of blood-CNS exchange. The structure and function of the BBB is summarised, the physical barrier formed by the endothelial tight junctions, and the transport barrier resulting from membrane transporters and vesicular mechanisms. The roles of associated cells are outlined, especially the endfeet of astrocytic glial cells, and pericytes and microglia. The embryonic development of the BBB, and changes in pathology are described. The BBB is subject to short and long-term regulation, which may be disturbed in pathology. Any programme for drug discovery or delivery, to target or avoid the CNS, needs to consider the special features of the BBB.

Control protocol for robust in vitro glial scar formation around microwires: essential roles of bFGF and serum in gliosis

Previously, we reported an in vitro cell culture model that recreates many of the hallmarks of glial scarring around electrodes used for recording in the brain; however, the model lacked the reproducibility necessary to establish a useful characterization tool. This methods paper describes a protocol, modeled on protocols typically used to culture neural stem/precursor cells, that generates a predictable positive control of an intense scarring reaction. Six independent cell culture variables (growth media, seeding density, bFGF addition day, serum concentration in treatment media, treatment day, and duration of culture) were varied systematically and the resulting scars were quantified. The following conditions were found to give the highest level of scarring: Neurobasal medium supplemented with B27, 10% fetal bovine serum at treatment, 10 ng/ml b-FGF addition at seeding and at treatment, treatment at least 6 days after seeding and scar growth of at least 5 days. Seeding density did not affect scarring as long as at least 500,000 cells were seeded per well, but appropriate media, bFGF, and serum were essential for significant scar formation-insights that help validate the in vitro-based approach to understanding glial scarring. With the control protocol developed in this study producing a strong, reproducible glial scarring positive control with every dissection, this culture model is suitable for the in vitro study of the mechanisms behind glial scarring and neuroelectrode failure.

Permeability of the blood-brain barrier depends on brain temperature

Increased permeability of the blood-brain barrier (BBB) has been reported in different conditions accompanied by hyperthermia, but the role of brain temperature per se in modulating brain barrier functions has not been directly examined. To delineate the contribution of this factor, we examined albumin immunoreactivity in several brain structures (cortex, hippocampus, thalamus and hypothalamus) of pentobarbital-anesthetized rats (50 mg/kg i.p.), which were passively warmed to different levels of brain temperature (32-42 degrees C). Similar brain structures were also examined for the expression of glial fibrillary acidic protein (GFAP), an index of astrocytic activation, water and ion content, and morphological cell abnormalities. Data were compared with those obtained from drug-free awake rats with normal brain temperatures (36-37 degrees C). The numbers of albumin- and GFAP-positive cells strongly correlate with brain temperature, gradually increasing from approximately 38.5 degrees C and plateauing at 41-42 degrees C. Brains maintained at hyperthermia also showed larger content of brain water and Na(+), K(+) and Cl(-) as well as structural abnormalities of brain cells, all suggesting acute brain edema. The latter alterations were seen at approximately 39 degrees C, gradually progressed with temperature increase, and peaked at maximum hyperthermia. Temperature-dependent changes in albumin immunoreactivity tightly correlated with GFAP immunoreactivity, brain water, and numbers of abnormal cells; they were found in each tested area, but showed some structural specificity. Notably, a mild BBB leakage, selective glial activation, and specific cellular abnormalities were also found in the hypothalamus and piriform cortex during extreme hypothermia (32-33 degrees C); in contrast to hyperthermia these changes were associated with decreased levels of brain water, Na(+) and K(+), suggesting acute brain dehydration. Therefore, brain temperature per se is an important factor in regulating BBB permeability, alterations in brain water homeostasis, and subsequent structural abnormalities of brain cells.

Blood-brain barrier breakdown-inducing astrocytic transformation: novel targets for the prevention of epilepsy

Epileptogenesis is common following brain insults such as trauma, ischemia and infection. However, the mechanisms underlying injury-related epileptogenesis remain unknown. Recent studies demonstrated impaired integrity of the blood-brain barrier (BBB) during epileptogenesis. Here we review accumulating experimental evidence supporting the potential involvement of primary BBB lesion in epileptogenesis. Data from animal experiments demonstrate that primary breakdown of the BBB prone animals to develop focal neocortical epilepsy that is followed by neuronal loss and impaired functions. The extravasation of albumin from the circulation into the brain neuropil was found to be sufficient for the induction of epileptogenesis. Albumin binds to transforming growth factor beta receptor 2 (TGFbetaR2) in astrocytes and induces rapid transcriptional modifications, astrocytic transformation and dysfunction. We highlight a novel cascade of events which is initiated by increased BBB permeability, eventually leading to neuronal dysfunction, epilepsy and cell loss. We review potential mechanisms and existing experimental evidence for the important role of astrocytes and the TGFbeta pathway in epileptogenesis. Finally, we review evidence from human clinical data supporting the involvement of BBB lesion in epilepsy. We propose that primary vascular injury, and specifically BBB breakdown and repair, are key elements in altered interactions within the neurovascular unit and thus may serve as new therapeutic targets.

Progress and problems in the application of focused ultrasound for blood-brain barrier disruption

Advances in neuroscience have resulted in the development of new diagnostic and therapeutic agents for potential use in the central nervous system (CNS). However, the ability to deliver the majority of these agents to the brain is limited by the blood-brain barrier (BBB), a specialized structure of the blood vessel wall that hampers transport and diffusion from the blood to the brain. Many CNS disorders could be treated with drugs, enzymes, genes, or large-molecule biotechnological products such as recombinant proteins, if they could cross the BBB. This article reviews the problems of the BBB presence in treating the vast majority of CNS diseases and the efforts to circumvent the BBB through the design of new drugs and the development of more sophisticated delivery methods. Recent advances in the development of noninvasive, targeted drug delivery by MRI-guided ultrasound-induced BBB disruption are also summarized.

Albumin-stimulated DNA synthesis is mediated by Ca2+/PKC as well as EGF receptor-dependent p44/42 MAPK and NF-κB signal pathways in renal proximal tubule cells

It is now recognized that significant tubular reabsorption of albumin occurs under physiological conditions that may play an important role in maintaining proximal tubular integrity and function. Therefore, this study examined the effect of bovine serum albumin (BSA) on DNA synthesis and its related signal molecules in primary cultured rabbit renal proximal tubule cells (PTCs). BSA increased the level of [3H]thymidine incorporation in a dose (≥3 mg/ml)- and time (≥3 h)-dependent manner, intracellular Ca2+concentration, and the level of protein kinase C (PKC) phosphorylation and stimulated the phosphorylation of the epidermal growth factor receptor (EGFR), which was inhibited by EGTA (extracellular Ca2+chelator), 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid acetoxymethyl ester (BAPTA-AM, intracellular Ca2+chelator), or PKC inhibitors (staurosporine or bisindolylmaleimide I). In addition, the PKC inhibitors or an EGFR inhibitor (AG-1478) blocked the BSA-induced phosphorylation of p44/42 mitogen-activated protein kinases (MAPKs). BSA also increased the level of nuclear factor-κB (NF-κB) and inhibitor of NF-κB (IκB) phosphorylation, which was blocked by staurosporine, AG-1478, or PD-98059 (p44/42 MAPK inhibitor). Inhibition of Ca2+, PKC, EGFR, p44/42 MAPK, or NF-κB signal pathways blocked the BSA-induced incorporation of [3H]thymidine. Consequently, the inhibition of Ca2+, PKC, EGFR, p44/42 MAPKs, or NF-κB blocked the BSA-induced increases in cyclin D1, cyclin-dependent kinase (CDK)4, cyclin E, or CDK2 and restored the BSA-induced inhibition of p21WAF/Cip1and p27Kip1expression. In conclusion, BSA stimulates DNA synthesis that is mediated by Ca2+/PKC as well as the EGFR-dependent p44/42 MAPK and NF-κB signal pathways in PTCs.

Nonviral approaches for neuronal delivery of nucleic acids

The delivery of therapeutic nucleic acids to neurons has the potential to treat neurological disease and spinal cord injury. While select viral vectors have shown promise as gene carriers to neurons, their potential as therapeutic agents is limited by their toxicity and immunogenicity, their broad tropism, and the cost of large-scale formulation. Nonviral vectors are an attractive alternative in that they offer improved safety profiles compared to viruses, are less expensive to produce, and can be targeted to specific neuronal subpopulations. However, most nonviral vectors suffer from significantly lower transfection efficiencies than neurotropic viruses, severely limiting their utility in neuron-targeted delivery applications. To realize the potential of nonviral delivery technology in neurons, vectors must be designed to overcome a series of extra- and intracellular barriers. In this article, we describe the challenges preventing successful nonviral delivery of nucleic acids to neurons and review strategies aimed at overcoming these challenges.

Astroglial injury in an ex vivo model: contributions to its analysis in enriched cell cultures

In vitro cell culture models have been proposed to analyze some of the complex structural and functional characteristics involved in astroglial changes after neural injury in vivo. This report contributes to analyze the proposed hypothesis that an experimentally induced discontinuity of a confluent cellular culture could represent a useful model for the analysis of the processes involved in a neural lesion. For this purpose, it was decided to characterize astroglial proliferation and dye coupling state after a "scratch wound" applied to confluent, astrocyte-enriched cell cultures, obtained from several rat brain regions. Proliferation was assessed in terms of bromodeoxyuridine nuclear incorporation as a function of lesion width, serum deprivation, time after confluence, brain region origin, postlesional culture medium changes and agitation, and after application of a gap-junction uncoupling agent. The proliferative reaction after injury was neither cell type-specific nor brain region specific, nor was significantly affected by neither of the above-mentioned variables. Furthermore, injury failed to significantly affect the astroglial dye coupling state. Results suggest that the proliferative response observed under present conditions would depend on the disruption of contact inhibition rather than on astroglial mitogenic signals released from the wound and operating by either extracellular or cell coupling mechanisms. Present results question the validity of astrocyte-enriched cell cultures as an experimental model of neural tissue injury in vivo, as they do not appear to reproduce fundamental characteristics expressed in situ.

Albumin-bound lipids induce free cytoplasmic calcium oscillations in human osteoblast-like cells

[Ca(2+)](i) oscillations were found in human osteoblast-like cells (hOB cells) exposed to high-lipid bovine serum albumin (BSA), but not when exposed to low-lipid BSA. These [Ca(2+)](i) oscillations were inhibited by heptanol and suramin, which implies that gap junctions and purinergic signalling may be important for these [Ca(2+)](i) oscillations. The high-lipid BSA preparation that was used contains arachidonic acid. [Ca(2+)](i) oscillations could be induced by low lipid albumin with arachidonic acid added. The albumin-bound lipids were also important for osteoblast growth since DNA synthesis and the total cell protein content was higher in hOB cells exposed to high-lipid BSA. The effect of arachidonic acid on hOB cell proliferation was bone-donor dependent; both stimulatory and inhibitory effects were observed. The physiological importance of albumin-bound lipids is unclear; given that albumin has only minimal contact with osteoblasts under normal conditions. Only when bone capillaries are disrupted, e.g. during a fracture, would significant amounts of albumin reach osteoblasts. Albumin-bound lipids could therefore contribute to stimulation of osteoblast proliferation during fracture healing.

Blood-brain barrier delivery

Neuropharmaceutics is the largest potential growth sector of the pharmaceutical industry. However, this growth is blocked by the problem of the blood-brain barrier (BBB). Essentially 100% of large-molecule drugs and >98% of small-molecule drugs do not cross the BBB. The BBB can be traversed because there are multiple endogenous transporters within this barrier. Therefore, brain drug development programs of the future need to be re-configured so that drugs are formulated to enable transport into the brain via endogenous BBB transporters.

Albumin prevents mitochondrial depolarization and apoptosis elicited by endoplasmic reticulum calcium depletion of neuroblastoma cells

Serum albumin protects against cell death elicited by various cytotoxic agents; however, conflicting views on the protective mechanism still remain. Hence, we have studied the ability of serum albumin to prevent apoptosis of human neuroblastoma SH-SY 5 Y cells elicited by four compounds known to release Ca(2+) from the endoplasmic reticulum, i.e. dotarizine, flunarizine, thapsigargin and cyclopiazonic acid. Spontaneous basal apoptosis, after 24 h incubation in Dulbecco's Modified Eagle Medium (DMEM) containing 10% serum, was 5%. Dotarizine (30--50 microM) enhanced basal apoptosis to 18--43%, flunarizine (30--50 microM) to 15%, thapsigargin (1--10 microM) to 21--35%, and cyclopiazonic acid (100 microM) to 10%. Serum deprivation augmented basal apoptosis to 20%. Under serum-free medium, 30 microM dotarizine or flunarizine drastically enhanced apoptosis to 63% and 68%, respectively; the increase was milder with 1 microM thapsigargin (37%) and 30 microM cyclopiazonic acid (27%). In serum-free medium, albumin (29 or 49 mg/ml) fully prevented the apoptotic effects of dotarizine, flunarizine and cyclopiazonic acid. The four compounds increased the cytosolic Ca(2+) concentration ([Ca(2+)](c)) in fluo-4 loaded cells; such increase developed slowly to reach a plateau after several minutes, followed by a slow decline. Albumin did not modify the kinetic parameters of such increase. In the absence of serum, dotarizine, flunarizine, thapsigargin, and cyclopiazonic acid caused mitochondrial depolarization in tetramethylrhodamine ethyl ester (TMRE)-loaded cells; depolarization was inhibited by cytoprotective concentrations of albumin. These results suggest that albumin protects cells from entering into apoptosis by preventing mitochondrial depolarization. They also suggest that inhibition of mitochondrial depolarization might become a target to develop new anti-apoptotic compounds with therapeutic neuroprotective potential in stroke, Alzheimer's disease, and other neurodegenerative diseases.

The blood-brain barrier: bottleneck in brain drug development

The blood-brain barrier (BBB) is formed by the brain capillary endothelium and excludes from the brain approximately 100% of large-molecule neurotherapeutics and more than 98% of all small-molecule drugs. Despite the importance of the BBB to the neurotherapeutics mission, the BBB receives insufficient attention in either academic neuroscience or industry programs. The combination of so little effort in developing solutions to the BBB problem, and the minimal BBB transport of the majority of all potential CNS drugs, leads predictably to the present situation in neurotherapeutics, which is that there are few effective treatments for the majority of CNS disorders. This situation can be reversed by an accelerated effort to develop a knowledge base in the fundamental transport properties of the BBB, and the molecular and cellular biology of the brain capillary endothelium. This provides the platform for CNS drug delivery programs, which should be developed in parallel with traditional CNS drug discovery efforts in the molecular neurosciences.

Albumin stimulates monocyte chemotactic protein-1 expression in rat embryonic mixed brain cells

Albumin, a blood protein absent from the adult brain in physiological situations, can be brought into contact with brain cells during development or, in adult, following breakdown of the blood-brain barrier occurring as a result of local inflammation. In the present study, we show that ovalbumin and albumin induce the release of monocyte chemotactic protein 1 (MCP-1/CCL2) from rat embryonic mixed brain cells. A short-term exposure to ovalbumin during the cell dissociation procedure is sufficient to generate MCP-1 mRNA. A comparable effect is observed when the cells are incubated for 4 hr with ovalbumin or rat albumin, while MCP-1 messengers are barely detectable following bovine albumin exposure. The amount of MCP-1 protein measured in 4 hr-supernatants of albumin-treated cells followed the same albumin-inducing pattern as that of MCP-1 mRNA, while all albumins tested induced MCP-1 protein after a 17 hr-incubation period. The albumin-induced MCP-1 production is significantly inhibited in calphostin C-treated cells, suggesting the implication of a protein kinase C-dependent signaling pathway. This MCP-1-inducing activity is maintained after a lipid extraction procedure but abolished by proteinase K or trypsin treatments of albumin. The MCP-1 secretion following albumin contact with nervous cells could thus interfere, by chemotactic gradient formation, with the brain infiltration program of blood-derived cells during development or brain injury.

Ectodermal commitment of insulin‐producing cells derived from mouse embryonic stem cells

Embryonic stem cells possess the ability to differentiate in vitro into a variety of cell lineages, including insulin-producing cells. Pancreatic beta-cells derive from foregut endoderm during embryonic development. However, previous reports using transgenic mice strongly indicate that insulin-positive cells may be generated also through the neuroectoderm pathway. To analyze this point, a culture system was performed in which only ectoderm committed cells were present. Based on published work, we achieved this by maintaining transfected clonal R1 mouse embryonic stem cells in monolayer in the absence of LIF. Contrary to differentiation protocols via embryoid body formation, monolayer cultured cells displayed ectodermal fates according to the marker gene expression pattern. Under these particular conditions, neomycin was added in order to select insulin-expressing cells. The cell lineage obtained expressed Pdx1, Pax6, Isl1, AChE, MBP, TH, and GS genes, confirming ectodermal commitment, even though some of these factors are also expressed in endoderm. In addition these cells displayed excitatory properties similar to astrocytes. Co-expression of insulin II and nestin was observed in monolayer culture and in the presence of specific conditioned media. No expression of early endodermal markers was detected along monolayer cultures. Altogether, these observations suggest that cells with ectoderm fates could participate in vitro in the derivation of insulin-producing cells. These results have implications for insulin gene regulation and hormone secretion in order to generate insulin-producing cells for replacement protocols in the treatment of diabetes.

Pure albumin is a potent trigger of calcium signalling and proliferation in microglia but not macrophages or astrocytes

Microglial activation is implicated in the neurotoxicity of neurodegenerative diseases. Raised intracerebral levels of albumin are associated with the pathology of Alzheimer's disease, multiple sclerosis, and stroke where blood-brain barrier damage is evident. We report here that treatment of primary cultured microglia and the N9 microglial cell line with pure albumin, or albumin in which fatty acids and immunoglobulins remain attached (fraction V), induced a rise in intracellular calcium. This rise in intracellular calcium was mediated via Src tyrosine kinase and phospholipase C. The albumin-induced calcium response was coupled to microglial proliferation, which was prevented by BAPTA, U73122 or PP2 but not mimicked by thapsigargin. In contrast, peritoneal macrophages were resistant to albumin- or fraction V-induced calcium responses and proliferation, whilst primary cultured astrocytes or the TSA-3 astrocyte cell line were responsive to fraction V albumin but not pure albumin. Furthermore, cerebellar granule neurones did not respond to albumin. These data suggest that albumin may play a role in microglial activation in pathological situations involving blood-brain barrier impairment, and that the specific responses of microglia to albumin allow a distinction to be made between the signalling responses of microglia, blood-borne macrophages, astrocytes and neurones.

The effects of magnesium sulfate on blood-brain barrier disruption caused by intracarotid injection of hyperosmolar mannitol in rats

The study was performed to evaluate whether magnesium sulfate could alter the degree of disruption of the blood-brain barrier (BBB) caused by hyperosmotic mannitol. Wistar adult female rats were infused with 25% mannitol into the left internal carotid artery. Each animal received intraperitoneally a 300 mg/kg loading dose of magnesium sulfate, dissolved in 0.9% saline, followed by a further 100 mg/kg dose. In the other group, intracarotid infusion of magnesium sulfate was performed at a dose of 150 mg/kg 10 min before mannitol administration. Evans blue (EB) dye was used as a marker of BBB disruption. The measured serum glucose and magnesium levels increased after mannitol and/or magnesium administration when compared with their initial values before treatment (P < 0.01). Water content of the left hemisphere was significantly increased by hyperosmotic mannitol (P < 0.01). The increased water content in the mannitol-perfused hemisphere was significantly decreased by magnesium treatment (P < 0.05). The content of EB dye in the mannitol-perfused hemisphere markedly increased when compared with the right hemisphere of the same brain (P < 0.01). The EB dye content in the mannitol-perfused hemisphere following both intraperitoneal and intraarterial administration of magnesium decreased when compared with mannitol alone (P < 0.01). We conclude that although magnesium sulfate administration by both intracarotid arterial and intraperitoneal routes attenuates BBB disruption caused by hyperosmolar mannitol, particularly intraperitoneal route of magnesium sulfate administration may provide a useful strategy to limit the transient osmotic opening of the BBB.

Modulation of the blood–brain barrier in oncology: therapeutic opportunities for the treatment of brain tumours?

Systemically administered chemotherapy is not very effective in the treatment of primary or metastatic brain tumours. An important reason for this low efficacy is insufficient drug delivery to the tumour site due to the presence of the blood-brain barrier (BBB). In this review, we give an overview of strategies that were tested to bypass the BBB or to increase its permeability for anticancer drugs. Local drug administration through intracerebral implants offers only little benefit to patients with brain tumours, probably due to the limited diffusion of the drugs in brain tissue. Temporary disruption of the BBB can be achieved with intracarotid infusions of hypertonic mannitol. This method has been used with some success; however, toxic side effects and the high complexity of the surgical procedure limit its usefulness. More recently, the use of the bradykinin agonist cereport was shown to be useful in preclinical studies, but unfortunately clinical studies did not show improved efficacy. Since P-glycoprotein in the BBB restricts the brain entry of many anticancer drugs, inhibition of this drug transporter may be an option for improved drug delivery to brain tumours. Pre-clinical studies have shown the feasibility to enhance the penetration of paclitaxel into the brain by co-administration with a potent P-glycoprotein inhibitor and further clinical research is warranted.

Gene therapy of the brain

Many chronic neurologic diseases do not respond to small molecule therapeutics, and have no effective long-term therapy. Gene therapy offers the promise of an effective cure for both genetic and acquired brain disease. However, the limiting problem in brain gene therapy is delivery to brain followed by regulation of the expression of the transgene. Present day gene vectors do not cross the blood-brain barrier (BBB). Consequently, brain gene therapy requires craniotomy and the local injection of a viral gene vector. However, there are few brain disorders that can be effectively treated with local injection. Most applications of gene therapy require global expression in the brain of the exogenous gene, and this can only be achieved with a noninvasive delivery through the BBB—the trans-vascular route to brain. An additional consideration is the potential toxicity of all viral and nonviral approaches, which may either integrate into the host genome and cause insertional mutagenesis or cause inflammation in the brain. Nonviral, noninvasive gene therapy of the brain is now possible with the development of a new approach to targeting therapeutic genes to the brain following an IV administration. This approach utilizes genetically engineered molecular Trojan horses, which ferry the gene across the BBB and into neurons. Global and reversible expression of therapeutic genes in the human brain without surgery and without viral vectors is now possible.

Drug and gene delivery to the brain: the vascular route

Brain drug development of either small molecule or large molecule (recombinant proteins, gene medicines) neurotherapeutics has been limited, owing to the restrictive transport properties of the brain microvasculature, which forms the blood-brain barrier (BBB) in vivo. Widespread drug delivery to the brain, while not feasible via craniotomy and intracerebral injection, is possible if the drug is delivered to brain via the transvascular route through the BBB. Novel brain drug delivery and drug targeting strategies can be developed from an understanding of the molecular and cellular biology of the brain microvascular and BBB transport processes.

Innovations in design and delivery of chemotherapy for brain tumors

Effectiveness of chemotherapy in patients with brain tumors is hampered by the presence of the blood-brain barrier and drug resistance. In recent years, significant progress has been made in devising innovative methods of design and delivery of chemotherapy for brain tumors. This article has surveyed the issues of blood-brain barrier and drug resistance and explored some of the strategies used to circumvent problems associated with chemotherapy failure in patients with brain tumors.

Reduction of plasma triglyceride level and enhancement of plasma albumin concentration by Oren-gedoku-to administration

Oren-gedoku-to (Huanglian-Jie-Du-Tang, OGT) has been used for the treatment of cerebrovascular disease, hypertension, gastritis and liver disease in Japan. The present study was to test whether ingestion of OGT extract (TJ-15) would affect the metabolism of fatty acids and the usual antioxidant molecule (such as albumin, uric acid and bilirubin) levels in human plasma. After the administration of TJ-15, plasma total cholesterol and the triglyceride level significantly decreased, and lipoprotein lipase mass increased. Significant enhancement of plasma albumin level and reduction of the total plasma protein level resulted in an increment of the albumin/globulin ratio. Plasma fibrinogen, an independent risk factor for cerebrovascular disease, declined considerably, but the reduction was not statistically significant. The findings of this study suggest that ingestion of TJ-15 improves the microcirculation through lipid and protein metabolisms, and is useful for the treatment of cerebral vascular attack in human.

Albumin promotes neuronal survival by increasing the synthesis and release of glutamate

It is well known that the presence of albumin within the brain and the CSF is developmentally regulated. However, the physiological relevance of this phenomenon is not well established. We have previously shown that albumin specifically increases the flux of glucose and lactate through the pyruvate dehydrogenase reaction in astrocytes. Here we show that, in neurones, albumin also increases the oxidation of glucose and lactate through the pyruvate dehydrogenase-catalysed reaction, the final purpose of this being the synthesis of glutamate. Thus, in neurones, the presence of albumin strongly increased the synthesis and release of glutamate to the extracellular medium. Our results also suggest that glutamate release caused by albumin is designed to promote neuronal survival. Thus, under culture conditions in which neurones die by apoptosis, the presence of albumin promoted neuronal survival and maintained the differentiation programme of these cells, as judged by the expression of the axonal protein, GAP-43. The effect of albumin on neuronal survival was counteracted by the presence of DNQX, an antagonist of non-NMDA-glutamate receptors, suggesting that the glutamate synthesized and released due to the presence of albumin is responsible for neuronal survival. In addition, the effect of albumin seemed to depend on the activity of the NGF receptor, TrkA, suggesting that the glutamate synthesized and released due to the presence of albumin promotes neuronal survival through the activity of TrkA.

Astrocyte-synthesized oleic acid behaves as a neurotrophic factor for neurons

Unlike in the adult brain, the newborn brain specifically takes up serum albumin during the postnatal period, coinciding with the stage of maximal brain development. Here we shall summarize our knowledge about the role played by albumin in brain development. The role of this protein in brain development is intimately related to its ability to carry fatty acids. Thus, albumin stimulates oleic acid synthesis by astrocytes from the main metabolic substrates available during brain development. Astrocytes internalize albumin in vesicle-like structures by receptor-mediated endocytosis, which is followed by transcytosis, including passage through the endoplasmic reticulum (ER). The presence of albumin in the ER activates the sterol regulatory element-binding protein-1 (SREBP-1) and increases stearoyl-CoA 9-desaturase (SCD) mRNA, the key enzyme in oleic acid synthesis. Oleic acid released by astrocytes is used by neurons for the synthesis of phospholipids and is specifically incorporated into growth cones. In addition, oleic acid promotes axonal growth, neuronal clustering, and the expression of the axonal growth associated protein, GAP-43. All of these observations indicate neuronal differentiation. The effect of oleic acid on GAP-43 synthesis is brought about by the activation of protein kinase C. The expression of GAP-43 is significantly increased by the presence of albumin in neurons co-cultured with astrocytes, indicating that neuronal differentiation takes place by the presence of oleic acid synthesized and released by astrocytes in situ. In conclusion, during brain development the presence of albumin could play an important role by triggering the synthesis and release of oleic acid by astrocytes, thereby inducing neuronal differentiation.

Neuronal differentiation is triggered by oleic acid synthesized and released by astrocytes

Unlike in the adult brain, the newborn brain specifically takes up serum albumin during the postnatal period, coinciding with the stage of maximal brain development. Here we report that albumin stimulates oleic acid synthesis by astrocytes from the main metabolic substrates available during brain development. Oleic acid released by astrocytes is used by neurons for the synthesis of phospholipids and is specifically incorporated into growth cones. Oleic acid promotes axonal growth, neuronal clustering, and expression of the axonal growth-associated protein-43, GAP-43; all these observations indicating neuronal differentiation. The effect of oleic acid on GAP-43 synthesis is brought about by the activation of protein kinase C, since it was prevented by inhibitors of this kinase, such as H-7, polymyxin or sphingosine. The expression of GAP-43 was significantly increased in neurons co-cultured with astrocytes by the presence of albumin indicating that neuronal differentiation takes place in the presence of oleic acid synthesized and released by astrocytes in situ. In conclusion, during brain development the presence of albumin could play an important role by triggering the synthesis and release of oleic acid by astrocytes, which induces neuronal differentiation.

Diminution of metabolism/blood flow uncoupling following traumatic brain injury in rats in response to high-dose human albumin treatment

OBJECT

The authors have recently demonstrated that high-dose human albumin is markedly neuroprotective in experimental traumatic brain injury (TBI) and cerebral ischemia. The pathophysiology of TBI involves acute uncoupling of cerebral glucose utilization and blood flow. The intent of this study was to establish whether the use of human albumin therapy in a model of acute TBI would influence this phenomenon.

METHODS

Anesthetized, physiologically regulated rats received moderate (1.5-2 atm) fluid-percussion injury to the parietal lobe. Fifteen minutes after trauma or sham injury, rats in one group received human albumin (2.5 g/kg) administered intravenously and those in another group received 0.9% saline vehicle. At 60 minutes and 24 hours posttrauma, autoradiographic studies of local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCMRglu) were conducted, and the LCMRglu/LCBF ratio was determined. Sham-injured rats had normal levels of LCBF and LCMRglu, and no differences between vehicle- and albumin-treated rats were evident. Sixty minutes after TBI, LCBF was moderately reduced bilaterally in vehicle-treated rats, whereas in albumin-treated animals, the LCBF contralateral to the side of injury was generally normal. Despite acutely depressed LCBF, LCMRglu in vehicle-treated rats at 60 minutes was paradoxically normal bilaterally, and foci of elevated LCMRglu were noted in the ipsilateral hippocampus and thalamus. By contrast, in albumin-treated rats studied 60 minutes post-TBI, reduced LCMRglu values were measured in the ipsilateral caudoputamen and parietal cortex, whereas LCMRglu in other ipsilateral and contralateral sites did not differ from that measured in sham-injured animals. The metabolism/blood flow ratio was normal in sham-injured rats, but became markedly elevated in vehicle-treated rats 60 minutes post-TBI (on average, by threefold ipsilaterally and 2.1-fold contralaterally). By contrast, the mean metabolism/blood flow ratio in albumin-treated animals was elevated by only 1.6-fold ipsilaterally and was normal contralaterally. Twenty-four hours after TBI, LCBF contralateral to the side of injury had generally returned to normal levels in the albumin-treated group.

CONCLUSIONS

These results demonstrate that human albumin therapy benefits the posttraumatic brain by diminishing the pronounced metabolism > blood flow dissociation that would otherwise occur within the 1st hour after injury. Viewed together with our previous evidence of histological neuroprotection, these findings indicate that human albumin therapy may represent a desirable treatment modality for acute TBI.

Human albumin therapy of acute ischemic stroke: marked neuroprotective efficacy at moderate doses and with a broad therapeutic window

BACKGROUND AND PURPOSE

We examined the neuroprotective efficacy of moderate-dose human albumin therapy in acute focal ischemic stroke and defined the therapeutic window after stroke onset, within which this therapy would confer neurobehavioral and histopathological neuroprotection.

METHODS

Sprague-Dawley rats were anesthetized with halothane/nitrous oxide and received 2-hour middle cerebral artery occlusion (MCAo) by a poly-L-lysine-coated intraluminal suture. Neurological status was evaluated during occlusion (60 minutes) and daily for 3 days after MCAo. In the dose-response study, human albumin doses of either of 0.63 or 1.25 g/kg or saline vehicle (5 mL/kg) were given intravenously immediately after suture removal. In the therapeutic window study, a human albumin dose of 1.25 g/kg was administered intravenously at 2 hours, 3 hours, 4 hours, or 5 hours after onset of MCAo. Three days after MCAo, brains were perfusion-fixed, and infarct volumes and brain swelling were determined.

RESULTS

Moderate-dose albumin therapy significantly improved the neurological score at 24 hours, 48 hours, and 72 hours and significantly reduced total infarct volume (by 67% and 58%, respectively, at the 1.25- and 0.63-g/kg doses). Cortical and striatal infarct volumes were also significantly reduced by both doses. Brain swelling was virtually eliminated by albumin treatment. Even when albumin therapy (1.25 g/kg) was initiated as late as 4 hours after onset of MCAo, it improved the neurological score and markedly reduced infarct volumes in cortex (by 68%), subcortical regions (by 52%), and total infarct (by 61%).

CONCLUSIONS

Moderate-dose albumin therapy markedly improves neurological function and reduces infarction volume and brain swelling, even when treatment is delayed up to 4 hours after onset of ischemia.

Quinolinic acid enhances permeability of rat brain microvessels to plasma albumin

Several studies have established that increased cerebrospinal fluid (CSF) levels of quinolinic acid (QUIN), a macrophage/microglia-derived excitotoxin with N-methyl-D-aspartate (NMDA)-receptor affinity, may reflect abnormal blood-brain barrier (BBB) function in patients with acquired immunodeficiency syndrome (AIDS) dementia complex, exhibiting a relationship to their clinical and neurological status. This study was aimed to evaluate whether QUIN (250 nmol/0.25 microl/ventricle) infused into both lateral cerebral ventricles permeates adult rat brain microvessels to plasma albumin. Possible BBB dysfunction was examined 4 days after the intracerebroventricular (i.c.v.) infusion of QUIN by measuring plasma albumin extravasation using rocket immunoelectrophoresis. The i.c.v. infusion of QUIN failed to increase the extracellular tissue concentration of albumin in the entorhinal cortex, but significantly higher levels were found in the hippocampus proper (but not in the subiculum region and dentate gyrus) and in the striatum. To evaluate the possible relationship between plasma protein extravasation and QUIN-induced tissue necrosis, we quantified neuronal death in the rat hippocampal formation (subiculum, CA1/CA3 areas of the hippocampus proper, dentate gyrus). We found significantly higher tissue levels of plasma albumin in the hippocampus proper, in which the CA1 area exhibited the highest neuronal loss while the low rate of neuronal death was not accompanied by significant albumin extravasation in the dentate gyrus. However, in case of the subiculum, in which the neuronal loss reached comparable values to those in the CA1 area, we did not find significant enhancement of plasma albumin leakage into this area. The regional differences in brain microvascular permeability may depend on the density of NMDA receptors in the multicellular capillary barrier, but the differences in neuronal death may also reflect an involvement of NMDA receptors in neuronal membranes. We conclude that increased CSF QUIN levels evoke a dysfunction of the BBB that may only partially be related to sites with pronounced neuronal damage in the rat brain regions susceptible to NMDA-receptor mediated toxicity.

The nature and composition of the internal environment of the developing brain

1. The fetal brain develops within its own environment, which is protected from free exchange of most molecules among its extracellular fluid, blood plasma, and cerebrospinal fluid (CSF) by a set of mechanisms described collectively as "brain barriers." 2. There are high concentrations of proteins in fetal CSF, which are due not to immaturity of the blood-CSF barrier (tight junctions between the epithelial cells of the choroid plexus), but to a specialized transcellular mechanism that specifically transfers some proteins across choroid plexus epithelial cells in the immature brain. 3. The proteins in CSF are excluded from the extracellular fluid of the immature brain by the presence of barriers at the CSF-brain interfaces on the inner and outer surfaces. These barriers are not present in the adult. 4. Some plasma proteins are present within the cells of the developing brain. Their presence may be explained by a combination of specific uptake from the CSF and synthesis in situ. 5. Information about the composition of the CSF (electrolytes as well as proteins) in the developing brain is of importance for the culture conditions used for experiments with fetal brain tissue in vitro, as neurons in the developing brain are exposed to relatively high concentrations of proteins only when they have cell surface membrane contact with CSF. 6. The developmental importance of high protein concentrations in CSF of the immature brain is not understood but may be involved in providing the physical force (colloid osmotic pressure) for expansion of the cerebral ventricles during brain development, as well as possibly having nutritive and specific cell development functions.

Affinity chromatography of plasma proteins (guanidinobenzoatase): use of mimetic matrices and mimetic soluble ligands to prevent the binding of albumin on target affinity matrices

Serum albumin is the most abundant protein in plasma and it has a high capacity to bind many small compounds and macromolecules. In this way, albumin may promote important interferences during affinity chromatography of plasma proteins. Guanidinobenzoatase (GB) is a very relevant plasma protease that seems to be related to tumoral processes. This enzyme may be adsorbed on tailor-made agmatine-amide-agarose (CH-A) supports (e.g., the ones having 2 micromol of guanidino groups per ml of agarose attached to the support, through a 6 C aliphatic chain). Such tailor-made supports containing a very low concentration of ionized groups are hardly able to adsorb any protein by anion-exchange. However, they are able to strongly adsorb albumin. In order to solve this problem new mimetic affinity matrices have been designed: (i) by using the same ligand immobilized through a different chemical linkage [guanidino groups attached via secondary amino bonds, (AEA)] or (ii) by using slightly different ligands (e.g., 1,8-octanediamine containing a primary amino group instead of a guanidino one) also attached to the support via amido bonds (CH-DAO). Albumin adsorbs on the target and on the two mimetic matrices while GB is mainly adsorbed on the target one. Moreover, the adsorption of albumin on the affinity matrix (CH-A) is very strongly inhibited by the presence of low concentrations of soluble ligands (e.g., 1,8-octanediamine containing two ionized primary amino groups). On the contrary, the adsorption of GB on CH-A is hardly inhibited by the presence of such mimetic soluble ligand. In this way, the former offering of crude GB samples to AEA plus the use of mimetic inhibitors during adsorption of the extract on CH-A completely prevent the undesirable adsorption of albumin. In a such way, an extremely selective adsorption of GB can be performed. Such an improved chromatography procedure allows a very easy affinity purification and detection of GB.

Diffusion-weighted magnetic resonance imaging confirms marked neuroprotective efficacy of albumin therapy in focal cerebral ischemia

BACKGROUND AND PURPOSE

We have recently shown high-dose human serum albumin therapy to confer marked histological protection in experimental middle cerebral artery occlusion (MCAo). We have now used diffusion-weighted magnetic resonance imaging (DWI) in conjunction with morphological methods to expand our understanding of this therapeutic approach.

METHODS

Physiologically controlled Sprague-Dawley rats received 2-hour MCAo by the modified intraluminal suture method. Treated rats received 25% human serum albumin solution (1% by body weight) immediately after the MCA was reopened. Vehicle-treated rats received saline. Computer-based image averaging was used to analyze DWI data obtained 24 hours after MCAo and light-microscopic histopathology obtained at 3 days. In a matched series, plasma osmolality and colloid oncotic pressure, as well as brain water content, were determined.

RESULTS

Albumin therapy, which lowered the hematocrit on average by 37% and raised plasma colloid oncotic pressure by 56%, improved the neurological score throughout the 3-day survival period. Within the ischemic focus, the apparent diffusion coefficient (ADC) computed from DWI data declined by 40% in vehicle-treated rats but was preserved at near-normal levels (8% decline) in albumin-treated rats (P<0.001). Albumin also led to higher ADC values within unlesioned brain regions. Histology revealed large consistent cortical and subcortical infarcts in vehicle-treated rats, while albumin therapy reduced infarct volume at these sites, on average, by 84% and 33%, respectively. Total infarct volume was reduced by 66% and brain swelling was virtually eliminated by albumin treatment. Microscopically, while infarcted regions of vehicle-treated rats had the typical changes of pannecrosis, infarcted zones of albumin-treated brains showed persistence of vascular endothelium and prominent microglial activation, suggesting that albumin therapy may help to preserve the neuropil within zones of residual infarction.

CONCLUSIONS

These findings confirm the striking neuroprotective efficacy of albumin therapy in focal cerebral ischemia and reveal that this effect is associated with DWI normalization and a mitigation of pannecrotic changes within zones of residual injury.

Modulation of arachidonic acid release and membrane fluidity by albumin in vascular smooth muscle and endothelial cells

Albumin is the major plasma protein circulating in blood. Albumin potently decreases capillary permeability, although the mechanisms are not understood completely. Albumin also effectively binds arachidonic acid (AA), which increases capillary permeability. To investigate the interactions of BSA and AA with the cell membrane, the effect of these substances on [3H]AA release and membrane fluidity was studied in vascular myocytes and endothelial cells. BSA (0.2 and 1 mg . mL-1) stimulated a significant release of [3H]AA from both intact rat aorta and cultured smooth muscle cells. This effect was not mimicked by gamma-globulin or myoglobin (both 1 mg . mL-1) in intact tissue. BSA, but not gamma-globulin and myoglobin, decreased the membrane fluidity (assessed as changes in the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3, 5-hexatriene) in a concentration-dependent manner with a half-maximum concentration between 0.007 and 0.4 mg . mL-1 in both freshly isolated and cultured rat aortic myocytes and human umbilical vein endothelial cells. AA (1 to 200 micromol/L) caused the opposite effect, increasing membrane fluidity and antagonizing the effect of BSA. BSA modified at its arginine residues, which are thought to be important in AA binding, did not stimulate [3H]AA release and was significantly less potent than native BSA in altering the membrane fluidity. The effect of BSA can be explained by a high-affinity binding of AA to the protein and extraction of AA from the cell membrane. The interaction between BSA and AA could play a role in the regulation of vascular permeability.

The effect of high-dose albumin therapy on local cerebral perfusion after transient focal cerebral ischemia in rats

We have shown that high-concentration albumin therapy is markedly neuroprotective in focal cerebral ischemia. The present study was conducted to ascertain the degree to which hemodynamic alterations are responsible for this therapeutic effect. Normothermic, physiologically regulated male Sprague-Dawley rats received a 2-h period of middle cerebral artery occlusion (MCAo) by insertion of an intraluminal suture coated with poly-L-lysine. Albumin (25% human serum albumin solution) or vehicle (0.9% sodium chloride) was administered intravenously at a dose of 1% of body weight immediately after suture withdrawal following 2-h MCAo. Local cerebral blood flow (LCBF) was measured autoradiographically with 14C-iodoantipyrine after 1 h of recirculation. Novel image-processing methods were used to compare average LCBF data sets against previously obtained infarction-frequency data on a pixel-by-pixel basis. Albumin therapy reduced mean hematocrit by 42% but produced no other systemic alterations. Pixel-based histopathological analysis revealed large, consistent cortical and subcortical infarcts in saline-treated rats with MCAo; albumin therapy reduced mean cortical infarct volume by 85%. Within regions showing albumin-associated neuroprotection, numbers of pixels having LCBF in the upper ischemic-core flow range (0.12-0.24 ml g-1 min-1) were reduced by 8.6-fold by albumin therapy when compared to saline-treated rats; and numbers of pixels with LCBF in the lower penumbral flow range (0.24-0.36 ml g-1 min-1) were reduced by 3. 1-fold in albumin-treated rats (p=0.04 by repeated-measures analysis of variance). Analysis of the [albumin-saline] 3-dimensional difference-image data set revealed a circumferential zone of statistically significant albumin-associated LCBF increase within the posterior portion of the ischemic hemisphere, surrounding the core-region of prior ischemia. Thus, high-concentration albumin therapy improves local perfusion to regions of critical LCBF reduction. The spatial extent of this LCBF effect, however, appears too small to account fully for the marked neuroprotective efficacy of this therapy. We suggest that other, non-hemodynamic mechanisms may also be contributory.

Albumin elicits calcium signals from astrocytes in brain slices from neonatal rat cortex

1. Albumin causes calcium signals and mitosis in cultured astrocytes, but it has not been established whether astrocytes in intact brain also respond to albumin. The effect of albumin on intracellular calcium concentration ([Ca2+]i) in single cells was therefore studied in acutely isolated cortical brain slices from the neonatal rat. 2. Physiological concentrations of albumin from plasma and from serum produced an increase in [Ca2+]i in a subpopulation of cortical cells. Trains of transient elevations in [Ca2+]i (Ca2+ spikes) were seen in 41 % of these cells. 3. The cells responding to albumin are identified as astrocytes because the neurone-specific agonist NMDA caused much smaller and slower responses in these cells. On the other hand NMDA-responsive cells, which are probably neurones, exhibited only small and slow responses to albumin. The residual responses of astrocytes to NMDA and neurones to albumin are likely to be due to crosstalk with adjacent neurones and astrocytes, respectively. 4. Methanol extraction of albumin removes a polar lipid and abolishes the ability of albumin to increase intracellular calcium. 5. Astrocyte calcium signalling caused by albumin may have important physiological consequences when the blood-brain barrier breaks down and allows albumin to enter the CNS.

Glial calcium: homeostasis and signaling function

Glial cells respond to various electrical, mechanical, and chemical stimuli, including neurotransmitters, neuromodulators, and hormones, with an increase in intracellular Ca2+ concentration ([Ca2+]i). The increases exhibit a variety of temporal and spatial patterns. These [Ca2+]i responses result from the coordinated activity of a number of molecular cascades responsible for Ca2+ movement into or out of the cytoplasm either by way of the extracellular space or intracellular stores. Transplasmalemmal Ca2+ movements may be controlled by several types of voltage- and ligand-gated Ca(2+)-permeable channels as well as Ca2+ pumps and a Na+/Ca2+ exchanger. In addition, glial cells express various metabotropic receptors coupled to intracellular Ca2+ stores through the intracellular messenger inositol 1,4,5-triphosphate. The interplay of different molecular cascades enables the development of agonist-specific patterns of Ca2+ responses. Such agonist specificity may provide a means for intracellular and intercellular information coding. Calcium signals can traverse gap junctions between glial cells without decrement. These waves can serve as a substrate for integration of glial activity. By controlling gap junction conductance, Ca2+ waves may define the limits of functional glial networks. Neuronal activity can trigger [Ca2+]i signals in apposed glial cells, and moreover, there is some evidence that glial [Ca2+]i waves can affect neurons. Glial Ca2+ signaling can be regarded as a form of glial excitability.