A proposed role for efflux transporters in the pathogenesis of hydrocephalus

Hydrocephalus is a common brain disorder that is treated only with surgery. The basis for surgical treatment rests on the circulation theory. However, clinical and experimental data to substantiate circulation theory have remained inconclusive. In brain tissue and in the ventricles, we see that osmotic gradients drive water diffusion in water-permeable tissue. As the osmolarity of ventricular CSF increases within the cerebral ventricles, water movement into the ventricles increases and causes hydrocephalus. Macromolecular clearance from the ventricles is a mechanism to establish the normal CSF osmolarity, and therefore ventricular volume. Efflux transporters, (p-glycoprotein), are located along the blood brain barrier and play an important role in the clearance of macromolecules (endobiotics and xenobiotics) from the brain to the blood. There is clinical and experimental data to show that macromolecules are cleared out of the brain in normal and hydrocephalic brains. This article summarizes the existing evidence to support the role of efflux transporters in the pathogenesis of hydrocephalus. The location of p-gp along the pathways of macromolecular clearance and the broad substrate specificity of this abundant transporter to a variety of different macromolecules are reviewed. Involvement of p-gp in the transport of amyloid beta in Alzheimer disease and its relation to normal pressure hydrocephalus is reviewed. Finally, individual variability of p-gp expression might explain the variability in the development of hydrocephalus following intraventricular hemorrhage.Hydrocephalus is a common brain disorder that affects children and individuals of all ages. It is the most common congenital abnormality in children (one out of 500 births) (1). If left untreated, hydrocephalus can lead to permanent brain damage and result in cognitive and physical handicap.Contemporary surgical management of hydrocephalus is based on the popular conceptualization of circulation theory. The circulation theory of hydrocephalus states that cerebrospinal fluid (CSF) produced by the choroid plexus flows along specific pathways to be absorbed by the venous sinuses. An obstruction in any part of these pathways leads to hydrocephalus. Surgical management of hydrocephalus is therefore directed at detecting and removing the source of obstruction (such as removal of tumor or blockage of pathways) or diverting the fluid bypassing the obstruction. As such, the most common treatment for hydrocephalus is the surgical implantation of a shunt system to divert the flow of CSF from the ventricles. However, although most cases of hydrocephalus are managed with a shunt system, it is rare for the device to last a lifetime without complications. Treatment of hydrocephalus leads to approximately 38 000 admissions per year in the US. Costs for treatment range from US $1.4-2 billion per year and approximately US $1 billion is spent on the revision of malfunctioning shunts (2).This may be a result of poor shunt design or a flawed approach to treatment.Circulation theory rests on the assumption that the brain parenchyma is impermeable to water, and is therefore incapable of independently absorbing the CSF that accumulates in the ventricles. However, we have previously seen that the brain is, in fact, permeable to water due to the presence of aquaporin channels and other ion channels (3,4). This permeability of brain parenchyma to water and several other observations question the validity and applicability of circulation theory to design treatment strategies for hydrocephalus.In brain tissue and in the ventricles, we see that osmotic gradients drive water diffusion in water permeable tissue. Alteration in osmolarity resulting from increase in the concentration of macromolecules and ions has been shown to increase the fluid content and hence the size of the ventricles (5-7). Any osmotic gradient between the ventricular or interstitial CSF and the blood is equilibrated with transport of water between the two compartments. Therefore, water movement into the ventricle is secondary to the presence of osmotic gradients due to excess macromolecules. Thus, water movement into and out of the ventricles is not independent but is dependent upon the presence and resolution of osmotic gradients due to increase or decrease in the macromolecular content (8).Within this article, we review the role played by osmotic gradients and macromolecular ventricular clearance in hydrocephalus. Macromolecular clearance from the ventricles is a mechanism to establish the normal CSF osmolarity, and therefore ventricular volume. At least two primary pathways of macromolecular ventricular clearance have been studied: paravascular pathways (also known as glymphatic pathways) and olfactory lymphatic pathways.In particular, we focus on the role played by efflux transporters, specifically p-gp (ABC-B1) in the pathogenesis of hydrocephalus. Efflux transporters are responsible for the transport and clearance of both endogenous (endobiotics) and exogenous (xenobiotics) substances. An understanding of these transporters is critical to designing effective pharmacological treatment for this problematic disorder.     

Vesicular glutamate transporters in the brain

Glutamate is an excitatory amino acid that acts as a major neurotransmitter throughout the brain. Although its neurotransmitter action has been evidenced by the identification of various receptor subtypes at synapses, a cellular mechanism by which this amino acid accumulates in synaptic vesicles has long been in doubt until the discovery in recent years of specific vesicular transporters. Three kinds of transporter isoforms have so far been cloned and their transport properties and distribution in the brain have been studied extensively. In contrast with the apparently similar ability of all transporter isoforms to highly selectively transport glutamate and their presence in synaptic vesicles, their regional distribution of gene expression and immunoreactivity in the rodent or human brain are surprisingly different from one another. This indicates that the glutamatergic neuron system of mammalian brains is substantially comprised of at least three different neuron subpopulations, each of which uses a unique transport system for the vesicular storage of glutamate. Thus, we now have highly useful and reliable tools for a comprehensive understanding of the glutamatergic neuron system in the brain from a new viewpoint different from that of other components, such as receptors. The scope of the present review is to provide an overview of the history and present status of the study of vesicular glutamate transporters and to highlight some unresolved issues requiring clarification for the progress of future brain function research.     

Role of glucocorticosteroids in the treatment of infectious diseases

The role of glucocorticosteroids in the management of infectious diseases in man remains controversial, although experimental data obtained both in in vitro systems and in experimental infections in animals provide evidence of a beneficial effect of such treatment. Their use in the treatment ofPneumocystic carinii pneumoniae and severe typhoid fever seems indicated. A beneficial effect on the treatment of bacterial meningitis needs to be confirmed. Sufficient data are now available that argue against steroid treatment in septic shock. However, new treatment modalities such as monoclonal antibodies against endotoxin and inflammatory mediators are currently being developed to modulate infectious inflammation. This could also bring a renaissance of the role of glucocorticosteroids in the treatment of infectious diseases.     

Role of glucocorticosteroids in the treatment of infectious diseases

The role of glucocorticosteroids in the management of infectious diseases in man remains controversial, although experimental data obtained both in in vitro systems and in experimental infections in animals provide evidence of a beneficial effect of such treatment. Their use in the treatment ofPneumocystic carinii pneumoniae and severe typhoid fever seems indicated. A beneficial effect on the treatment of bacterial meningitis needs to be confirmed. Sufficient data are now available that argue against steroid treatment in septic shock. However, new treatment modalities such as monoclonal antibodies against endotoxin and inflammatory mediators are currently being developed to modulate infectious inflammation. This could also bring a renaissance of the role of glucocorticosteroids in the treatment of infectious diseases.     

Functions of glutamate transporters in the brain

L-glutamate is the primary excitatory neurotransmitter in the mammalian central nervous system and has also been implicated as a potent neurotoxin. To ensure a high signal-to-noise ratio during synaptic transmission and to prevent neuronal damage that might occur as a result of excessive activation of glutamate receptors, the extracellular glutamate concentration is tightly controlled by glutamate transporters in the plasma membrane of neurons and the surrounding glial cells. Five subtypes of glutamate transporters have been identified and characterized by molecular cloning. Recent studies of glutamate transporters using the genetic knockout strategy indicate that glial, but not neuronal, glutamate transporters play critical roles in maintaining the extracellular glutamate concentrations and are thereby essential for both normal synaptic transmission at the photoreceptor synapses and protection of neurons against glutamate excitotoxicity. This review summarizes the current knowledge on the properties and functional roles of glutamate transporters, focusing on the properties of the anion channel in the transporters, the unexpected localization of these transporters, their role in synaptic transmission and plasticity, and their involvement in the protection of neurons against excitotoxicity.     

体重管理在骨科慢性病防治中的作用

目的:分析体重管理在骨科慢性病防治中的临床作用,为骨科慢性病患者建立良好的饮食和运动习惯.方法:选择2012年6月至2015年6月期间在南京军区南京总医院体检中发现的648例骨科慢性病患者,随机分为对照组和观察组,每组324例.对照组体检后继续现有饮食、运动习惯;观察组体检后进行严格的体重管理,包括个性化的膳食和运动锻炼指导,管理时间均为12个月.比较两组干预前后体重、关节疼痛感、关节活动功能等指标.结果:对照组干预前、干预后6个月、干预后12个月时各指标变化不显著(P＞0.05).观察组干预前、干预后6个月、干预后12个月时的肥胖情况差异显著(P＜0.05),其中以超重、肥胖比例变化最为明显.观察组干预前、干预6个月、干预12个月时的VAS评分(7.40±1.68 vs.6.94±1.42 vs.6.16±1.49)、BI指数(68.84±4.73 vs.74.82±5.33 vs.79.52±5.41)、关节功能优良率(56.48％ vs.65.74％ vs.75.00％)差异显著(P＜0.05).结论:体重管理干预能够有效改善患者的肥胖情况,减轻患者骨科慢性病症状,缓解疼痛,改善生活质量,值得临床重视.     

A passive MEMS drug delivery pump for treatment of ocular diseases

An implantable manually-actuated drug delivery device, consisting of a refillable drug reservoir, flexible cannula, check valve, and suture tabs, was investigated as a new approach for delivering pharmaceuticals to treat chronic ocular diseases. Devices are fabricated by molding and bonding three structured layers of polydimethylsiloxane. A 30 gauge non-coring needle was used to refill the reservoir; this size maximized the number of repeated refills while minimizing damage to the reservoir. The check valve cracking pressure was 76 ± 8.5 mmHg (mean ± SE, n = 4); the valve sustained > 2000 mmHg of reverse pressure without leakage. Constant delivery at 1.57 ± 0.2 μL/sec and 0.61 ± 0.2 μL/sec (mean ± SE, n = 4) under 500 mmHg and 250 mmHg of applied pressure, respectively, was obtained in benchtop experiments. The valve closing time constant was 10.2 s for 500 mmHg and 14.2 s for 250 mmHg. Assembled devices were successfully demonstrated in benchtop, ex vivo, and in vivo experiments.     

Distribution of norepinephrine transporters in the non-human primate brain

Noradrenergic terminals in the central nervous system are widespread; as such this system plays a role in varying functions such as stress responses, sympathetic regulation, attention, and memory processing, and its dysregulation has been linked to several pathologies. In particular, the norepinephrine transporter is a target in the brain of many therapeutic and abused drugs. We used the selective ligand [(3)H]nisoxetine, therefore, to describe autoradiographically the normal regional distribution of the norepinephrine transporter in the non-human primate central nervous system, thereby providing a baseline to which alterations due to pathological conditions can be compared. The norepinephrine transporter in the monkey brain was distributed heterogeneously, with highest levels occurring in the locus coeruleus complex and raphe nuclei, and moderate binding density in the hypothalamus, midline thalamic nuclei, bed nucleus of the stria terminalis, central nucleus of the amygdala, and brainstem nuclei such as the dorsal motor nucleus of the vagus and nucleus of the solitary tract. Low levels of binding to the norepinephrine transporter were measured in basolateral amygdala and cortical, hippocampal, and striatal regions. The distribution of the norepinephrine transporter in the non-human primate brain was comparable overall to that described in other species, however disparities exist between the rodent and the monkey in brain regions that play a role in such critical processes as memory and learning. The differences in such areas point to the possibility of important functional differences in noradrenergic information processing across species, and suggest the use of caution in applying findings made in the rodent to the human condition.     

Localization of equilibrative nucleoside transporters in the rat brain

Adenosine is a recognized inhibitory neuromodulator and neuroprotective agent in the central nervous system. It is produced both intra- and extracellularly and transported across the cell membrane. Nucleoside transporters thus have a major impact on the extracellular adenosine levels, and consequently adenosine signalling. We have raised and characterized polyclonal antibodies against both the equilibrative nucleoside transporters 1 and 2, and report for the first time their distribution in rat brain at the cellular level. Double staining studies were performed to assess the localization of the transporters in neural and glial cells. Both transporters were present in practically all neurons. Some astrocytes showed equilibrative nucleoside transporter 1 staining, while equilibrative nucleoside transporter 2 staining on astrocytes was observed only sporadically.     

Role of specific brain peptide factors in the pathogenesis and compensation of neurologic disorders and their use in the treatment of nervous system diseases]

New concepts of the molecular mechanisms implicated in the pathogenesis and compensation of central motor disorders are presented. It has been shown experimentally that specific peptide, postural asymmetry, and inactivation factors, play the leading part in these processes. The detection of these specific factors in the cerebrospinal fluid (CSF) of patients and convalescents allowed one to work out and test clinically a new method of treatment (CSF therapy) of patients with central motor disorders of varying genesis. The results of the clinical observations of two patients' groups (with cerebrovascular brain lesions and multiple sclerosis) are provided.     

MR spectroscopy: its potential role for drug development for the treatment of psychiatric diseases

Magnetic resonance spectroscopy (MRS) is likely in the near future to play a key role in the process of drug discovery and evaluation. As the pharmaceutical industry seeks biochemical markers of drug delivery, efficacy and toxicity, this non-invasive technique offers numerous ways to study adults and children repeatedly and without ionizing radiation. In this article, we survey an array of the information that MRS offers about neurochemistry in general and psychiatric disorders and their treatment in particular. We also present growing evidence of glial abnormalities in neuropsychiatric disorders and discuss what MRS is contributing to that line of investigation. The third major direction of this article is the discussion of where MRS techniques are headed and how those new techniques can contribute to studies of mechanisms of psychiatric disease and drug discovery.     

Immunohistochemical localization and quantification of glucose transporters in the mouse brain

A family of seven facilitative glucose transporters (Glut1-5, 7 and 8) mediates the cellular uptake of glucose. In the brain, Glut2, Glut5 and Glut8 are found at relatively low levels whereas Glut1, Glut3 and Glut4 were reported in abundance in several brain regions. Using immunofluorescence, this study investigated, compared and quantified the localization of the brain major glucose transporters, Glut1, Glut3 and Glut4, in the different cerebral areas of CD1 mice. Most of the staining of Glut1, Glut3 and Glut4 in the mouse brain coincides with observations made in rats. The results confirm the cortical neuropil distribution of Glut3, the prominence of this transporter in the mossy fiber field of the hippocampus and the Glut3 and Glut4 immunostaining of the hippocampal pyramidal cell layer. The present study also reports novel localizations of the transporters such as the presence of Glut3 in neuronal perikarya, Glut4-labeled neurons in the CA3 of the hippocampus and the subiculum. In the cerebellum, Glut3 shows subcellular localization to the base of the Purkinje cell bodies near the axon hillock. Furthermore, an important population of Golgi cells was found to be strongly immunostained for Glut4 in the granular cell layer of the cerebellum. The quantification results suggest that the relative abundance of Glut1 in the frontal and motor cortices coincides well with the high-energy demands of these brain regions. However, the Glut4-selective abundance in cerebral motor areas supports its suggested role in providing the energy needed for the control of the motor activity. The reported neuropil distribution of Glut3 seems to uphold its suggested role in synaptic energy provision and neurotransmitter synthesis.We conclude that the cellular and regional distributions of the glucose transporters in the rodent brain seem to be relevant to their corresponding functions.     

The ubiquitous ThrE family of putative transmembrane amino acid efflux transporters

We here report sequence analyses of a newly described family of putative amino acid exporters, the ThrE family. Homologues were identified in select bacteria, archaea and eukaryotes, but only in the fungal kingdom of eukaryotes. These proteins can exist either as single polypeptide chains or as pairs of polypeptide chains. Computational evidence suggests that these proteins exhibit 10 transmembrane alpha-helical segments (TMSs), having arisen from a five TMS precursor by an early intragenic duplication event. The phylogenetic tree of the ThrE family reveals that most proteins cluster according to organismal phylogeny with only a few exceptions, suggesting that the former proteins are orthologues. All family members exhibit hydrophilic N-terminal (and occasional C-terminal) extensions that show limited sequence similarity with a domain of unknown function found in many peptidases and proteases. The significance of these observations is discussed.     

Antidepressant drug treatment induces Arc gene expression in the rat brain

The mechanism underlying the therapeutic effect of antidepressants is not known but neuroadaptive processes akin to long-term potentiation have been postulated. Arc (Activity-regulated, cytoskeletal-associated protein) is an effector immediate early gene implicated in LTP and other forms of neuroplasticity. Recent data show that Arc expression is regulated by brain 5-hydroxytryptamine neurones, a target of many antidepressants. Here in situ hybridisation and immunohistochemistry were used to examine whether Arc expression in rat brain is altered by antidepressant drug treatment. Repeated administration of the monoamine reuptake inhibitors paroxetine, venlafaxine or desipramine induced region-specific increases in Arc mRNA. These increases were greatest in regions of the cortex (frontal and parietal cortex) and hippocampus (CA1 layer) and absent in the caudate putamen. Repeated treatment with the monoamine oxidase inhibitor, tranylcypromine, increased Arc mRNA in a similar fashion to the monoamine reuptake inhibitors. The antidepressant drugs also increased the number of Arc-immunoreactive cells in the parietal cortex. Acute antidepressant injection, and repeated administration of the antipsychotic drug chlorpromazine, produced either limited or no changes in Arc mRNA. The data suggest that chronic treatment with antidepressant drugs induces Arc gene expression in specific regions across the rat forebrain. Up-regulation of Arc expression may be part of the process by which antidepressant drugs achieve long-term changes in synaptic function in the brain.     

Vitamin transporters in mice brain with aging

Its high metabolic rate and high polyunsaturated fatty acid content make the brain very sensitive to oxidative damage. In the brain, neuronal metabolism occurs at a very high rate and generates considerable amounts of reactive oxygen species and free radicals, which accumulate inside neurons, leading to altered cellular homeostasis and integrity and eventually irreversible damage and cell death. A misbalance in redox metabolism and the subsequent neurodegeneration increase throughout the course of normal aging, leading to several age‐related changes in learning and memory as well as motor functions. The neuroprotective function of antioxidants is crucial to maintain good brain homeostasis and adequate neuronal functions. Vitamins E and C are two important antioxidants that are taken up by brain cells via the specific carriers αTTP and SVCT2, respectively. The aim of this study was to use immunohistochemistry to determine the distribution pattern of these vitamin transporters in the brain in a mouse model that shows fewer signs of brain aging and a higher resistance to oxidative damage. Both carriers were distributed widely throughout the entire brain in a pattern that remained similar in 4‐, 12‐, 18‐ and 24‐month‐old mice. In general, αTTP and SVCT2 were located in the same regions, but they seemed to have complementary distribution patterns. Double‐labeled cell bodies were detected only in the inferior colliculus, entorhinal cortex, dorsal subiculum, and several cortical areas. In addition, the presence of αTTP and SVCT2 in neurons was analyzed using double immunohistochemistry for NeuN and the results showed that αTTP but not SVCT2 was present in Bergmann's glia. The presence of these transporters in brain regions implicated in learning, memory and motor control provides an anatomical basis that may explain the higher resistance of this animal model to brain oxidative stress, which is associated with better motor performance and learning abilities in old age.     

Lactate efflux and the neuroenergetic basis of brain function.

In the unstimulated brain energy is primarily supplied by the oxidation of glucose. However the oxygen-to-glucose index (OGI), which is the ratio of metabolic rates of oxygen to glucose, CMR(O2)/CMR(glc), diverges from the theoretical value of 6 as activity is increased. In vivo measurements of brain lactate show its concentration to increase with stimulation. The decreasing OGI with stimulation had led to the suggestion that activation, unlike resting activity, is supported by anaerobic glycolysis. To date a unifying concept that accommodates glucose oxidation at rest with lactate generation and OGI decrease during stimulation of brain is lacking. Furthermore, energetics that change with increasing activity are not consistent with a neuroenergetic model that has been proposed from 1-(13)C-glucose MRS experiments. That model, based upon in vivo MRS measurements and cellular studies by Pellerin and Magistretti, showed that glutamate neurotransmitter cycling was coupled to glucose oxidation over a wide range of brain activities from rest down to deep anesthesia. Here we reconcile these paradoxical observations by suggesting that anaerobic glucose consumption (which can provide energy rapidly) increases with activation to meet the power requirements of millisecond neuronal firing. It is proposed, in accord with our neuroenergetic model, that the extra glucose mobilized rapidly for glial clearance of glutamate, is not needed for the oxidative processes that are responsible for neuronal firing and glutamate release, and consequently it is effluxed as lactate. A stoichiometric relation between OGI and lactate concentration is derived from the neuroenergetic model, showing that the enhanced glucose uptake during activation is consistent with neuronal activity being energetically supported by glucose oxidation.     

Role of the Klebsiella pneumoniae TolC porin in antibiotic efflux

The major Gram-negative gated efflux channel TolC has been extensively characterized in Escherichia coli but there is minimal information about Klebsiella pneumoniae TolC. Using an arabinose-inducible plasmid-based expression system, we show that the K. pneumoniae TolC complements the efflux defect in an E. coli K-12 ΔtolC strain, restoring wild-type levels of resistance towards most antibiotics suggesting that it can interact with the E. coli AcrB efflux pump. We characterize the efflux properties of K. pneumoniae TolC using an orthogonal whole cell-based assay and quantify the extrusion of environment-sensitive fluorescent probes and contrast the findings with the E. coli ortholog.