Choroid plexus epithelial expression of MDR1 P glycoprotein and multidrug resistance-associated protein contribute to the blood–cerebrospinal-fluid drug-permeability barrier

The blood–brain barrier and a blood–cerebrospinal-fluid (CSF) barrier function together to isolate the brain from circulating drugs, toxins, and xenobiotics. The blood–CSF drug-permeability barrier is localized to the epithelium of the choroid plexus (CP). However, the molecular mechanisms regulating drug permeability across the CP epithelium are defined poorly. Herein, we describe a drug-permeability barrier in human and rodent CP mediated by epithelial-specific expression of the MDR1 (multidrug resistance) P glycoprotein (Pgp) and the multidrug resistance-associated protein (MRP). Noninvasive single-photon-emission computed tomography with 99mTc-sestamibi, a membrane-permeant radiopharmaceutical whose transport is mediated by both Pgp and MRP, shows a large blood-to-CSF concentration gradient across intact CP epithelium in humans in vivo. In rats, pharmacokinetic analysis with 99mTc-sestamibi determined the concentration gradient to be greater than 100-fold. In membrane fractions of isolated native CP from rat, mouse, and human, the 170-kDa Pgp and 190-kDa MRP are identified readily. Furthermore, the murine proteins are absent in CP isolated from their respective mdr1a/1b(−/−) and mrp(−/−) gene knockout littermates. As determined by immunohistochemical and drug-transport analysis of native CP and polarized epithelial cell cultures derived from neonatal rat CP, Pgp localizes subapically, conferring an apical-to-basal transepithelial permeation barrier to radiolabeled drugs. Conversely, MRP localizes basolaterally, conferring an opposing basal-to-apical drug-permeation barrier. Together, these transporters may coordinate secretion and reabsorption of natural product substrates and therapeutic drugs, including chemotherapeutic agents, antipsychotics, and HIV protease inhibitors, into and out of the central nervous system.

Endothelin ETA receptor blockade restores NO-mediated endothelial function and inhibits atherosclerosis in apolipoprotein E-deficient mice

This study investigated whether endothelin-1 (ET-1), a potent vasoconstrictor, which also stimulates cell proliferation, contributes to endothelial dysfunction and atherosclerosis. Apolipoprotein E (apoE)-deficient mice and C57BL/6 control mice were treated with a Western-type diet to accelerate atherosclerosis with or without ETA receptor antagonist LU135252 (50 mg/kg/d) for 30 wk. Systolic blood pressure, plasma lipid profile, and plasma nitrate levels were determined. In the aorta, NO-mediated endothelium-dependent relaxation, atheroma formation, ET receptor-binding capacity, and vascular ET-1 protein content were assessed. In apoE-deficient but not C57BL/6 mice, severe atherosclerosis developed within 30 wk. Aortic ET-1 protein content (P < 0.0001) and binding capacity for ETA receptors was increased as compared with C57BL/6 mice. In contrast, NO-mediated, endothelium-dependent relaxation to acetylcholine (56 ± 3 vs. 99 ± 2%, P < 0.0001) and plasma nitrate were reduced (57.9 ± 4 vs. 93 ± 10 μmol/liter, P < 0.01). Treatment with the ETA receptor antagonist LU135252 for 30 wk had no effect on the lipid profile or systolic blood pressure in apoE-deficient mice, but increased NO-mediated endothelium-dependent relaxation (from 56 ± 3 to 93 ± 2%, P < 0.0001 vs. untreated) as well as circulating nitrate levels (from 57.9 ± 4 to 80 ± 8.3 μmol/liter, P < 0.05). Chronic ETA receptor blockade reduced elevated tissue ET-1 levels comparable with those found in C57BL/6 mice and inhibited atherosclerosis in the aorta by 31% without affecting plaque morphology or ET receptor-binding capacity. Thus, chronic ETA receptor blockade normalizes NO-mediated endothelial dysfunction and reduces atheroma formation independent of plasma cholesterol and blood pressure in a mouse model of human atherosclerosis. ETA receptor blockade may have therapeutic potential in patients with atherosclerosis.

Interference with gene regulation in living sea urchin embryos: Transcription factor Knock Out (TKO), a genetically controlled vector for blockade of specific transcription factors

“TKO” is an expression vector that knocks out the activity of a transcription factor in vivo under genetic control. We describe a successful test of this concept that used a sea urchin transcription factor of known function, P3A2, as the target. The TKO cassette employs modular cis-regulatory elements to express an encoded single-chain antibody that prevents the P3A2 protein from binding DNA in vivo. In normal development, one of the functions of the P3A2 transcription factor is to repress directly the expression of the CyIIIa cytoskeletal actin gene outside the aboral ectoderm of the embryo. Ectopic expression in oral ectoderm occurs if P3A2 sites are deleted from CyIIIa expression constructs, and we show here that introduction of an αP3A2⋅TKO expression cassette causes exactly the same ectopic oral expression of a coinjected wild-type CyIIIa construct. Furthermore, the αP3A2⋅TKO cassette derepresses the endogenous CyIIIa gene in the oral ectoderm and in the endoderm. αP3A2⋅TKO thus abrogates the function of the endogenous SpP3A2 transcription factor with respect to spatial repression of the CyIIIa gene. Widespread expression of αP3A2⋅TKO in the endoderm has the additional lethal effect of disrupting morphogenesis of the archenteron, revealing a previously unsuspected function of SpP3A2 in endoderm development. In principle, TKO technology could be utilized for spatially and temporally controlled blockade of any transcription factor in any biological system amenable to gene transfer.

Elimination of residual metastatic prostate cancer after surgery and adjunctive cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) blockade immunotherapy

Cancer relapse after surgery is a common occurrence, most frequently resulting from the outgrowth of minimal residual disease in the form of metastases. We examined the effectiveness of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) blockade as an adjunctive immunotherapy to reduce metastatic relapse after primary prostate tumor resection. For these studies, we developed a murine model in which overt metastatic outgrowth of TRAMP-C2 (C2) prostate cancer ensues after complete primary tumor resection. Metastatic relapse in this model occurs reliably and principally within the draining lymph nodes in close proximity to the primary tumor, arising from established metastases present at the time of surgery. Using this model, we demonstrate that adjunctive CTLA-4 blockade administered immediately after primary tumor resection reduces metastatic relapse from 97.4 to 44%. Consistent with this, lymph nodes obtained 2 weeks after treatment reveal marked destruction or complete elimination of C2 metastases in 60% of mice receiving adjunctive anti-CTLA-4 whereas 100% of control antibody-treated mice demonstrate progressive C2 lymph node replacement. Our study demonstrates the potential of adjunctive CTLA-4 blockade immunotherapy to reduce cancer relapse emanating from minimal residual metastatic disease and may have broader implications for improving the capability of immunotherapy by combining such forms of therapy with other cytoreductive measures including surgery.

Effects of muscarinic blockade in perirhinal cortex during visual recognition

Stimulus recognition in monkeys is severely impaired by destruction or dysfunction of the perirhinal cortex and also by systemic administration of the cholinergic-muscarinic receptor blocker, scopolamine. These two effects are shown here to be linked: Stimulus recognition was found to be significantly impaired after bilateral microinjection of scopolamine directly into the perirhinal cortex, but not after equivalent injections into the laterally adjacent visual area TE or into the dentate gyrus of the overlying hippocampal formation. The results suggest that the formation of stimulus memories depends critically on cholinergic-muscarinic activation of the perirhinal area, providing a new clue to how stimulus representations are stored.

Blockade of type β transforming growth factor signaling prevents liver fibrosis and dysfunction in the rat

We eliminated type β transforming growth factor (TGF-β) signaling by adenovirus-mediated local expression of a dominant-negative type II TGF-β receptor (AdCATβ-TR) in the liver of rats treated with dimethylnitrosamine, a model of persistent liver fibrosis. In rats that received a single application of AdCATβ-TR via the portal vein, liver fibrosis as assessed by histology and hydroxyproline content was markedly attenuated. All AdCATβ-TR-treated rats remained alive, and their serum levels of hyaluronic acid and transaminases remained at low levels, whereas all the AdCATβ-TR-untreated rats died of liver dysfunction. The results demonstrate that TGF-β does play a central role in liver fibrogenesis and indicate clearly in a persistent fibrosis model that prevention of fibrosis by anti-TGF-β intervention could be therapeutically useful.

Blockade of N-methyl-d-aspartate receptor activation suppresses learning-induced synaptic elimination

Auditory filial imprinting in the domestic chicken is accompanied by a dramatic loss of spine synapses in two higher associative forebrain areas, the mediorostral neostriatum/hyperstriatum ventrale (MNH) and the dorsocaudal neostriatum (Ndc). The cellular mechanisms that underlie this learning-induced synaptic reorganization are unclear. We found that local pharmacological blockade of N-methyl-d-aspartate (NMDA) receptors in the MNH, a manipulation that has been shown previously to impair auditory imprinting, suppresses the learning-induced spine reduction in this region. Chicks treated with the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (APV) during the behavioral training for imprinting (postnatal day 0–2) displayed similar spine frequencies at postnatal day 7 as naive control animals, which, in both groups, were significantly higher than in imprinted animals. Because the average dendritic length did not differ between the experimental groups, the reduced spine frequency can be interpreted as a reduction of the total number of spine synapses per neuron. In the Ndc, which is reciprocally connected with the MNH and not directly influenced by the injected drug, learning-induced spine elimination was partly suppressed. Spine frequencies of the APV-treated, behaviorally trained but nonimprinted animals were higher than in the imprinted animals but lower than in the naive animals. These results provide evidence that NMDA receptor activation is required for the learning-induced selective reduction of spine synapses, which may serve as a mechanism of information storage specific for juvenile emotional learning events.

Blockade of T-cell costimulation prevents development of experimental chronic renal allograft rejection.

Blocking CD28-B7 T-cell costimulation by systemic administration of CTLA4Ig, a fusion protein which binds B7 molecules on the surface of antigen-presenting cells, prevents rejection and induces tolerance in experimental acute allograft rejection models. We tested the effect of CTLA4Ig therapy on the process of chronic renal allograft rejection using an established experimental transplantation model. F344 kidneys were transplanted orthotopically into bilaterally nephrectomized LEW recipients. Control animals received low dose cyclosporine for 10 days posttransplantation. Administration of a single injection of CTLA4Ig on day 2 posttransplant alone or in addition to the low dose cyclosporine protocol resulted in improvement of long-term graft survival as compared with controls. More importantly, control recipients which received cyclosporine only developed progressive proteinuria by 8-12 weeks, and morphological evidence of chronic rejection by 16-24 weeks, including widespread transplant arteriosclerosis and focal and segmental glomerulosclerosis, while animals treated with CTLA4Ig alone or in addition to cyclosporine did not. Competitive reverse transcriptase-PCR and immunohistological analysis of allografts at 8, 16, and 24 weeks showed attenuation of lymphocyte and macrophage infiltration and activation in the CTLA4Ig-treated animals, as compared with cyclosporine-alone treated controls. These data confirm that early blockade of the CD28-B7 T-cell costimulatory pathway prevents later development and evolution of chronic renal allograft rejection. Our results indicate that T-cell recognition of alloantigen is a central event in initiating the process of chronic rejection, and that strategies targeted at blocking T-cell costimulation may prove to be a valuable clinical approach to preventing development of the process.

Glutamate receptor blockade at cortical synapses disrupts development of thalamocortical and columnar organization in somatosensory cortex.

The segregation of thalamocortical inputs into eye-specific stripes in the developing cat or monkey visual cortex is prevented by manipulations that perturb or abolish neural activity in the visual pathway. Such findings show that proper development of the functional organization of visual cortex is dependent on normal patterns of neural activity. The generalisation of this conclusion to other sensory cortices has been questioned by findings that the segregation of thalamocortical afferents into a somatotopic barrel pattern in developing rodent primary somatosensory cortex (S1) is not prevented by activity blockade. We show that a temporary block of N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors in rat S1 during the critical period for barrel development disrupts the topographic refinement of thalamocortical connectivity and columnar organization. These effects are evident well after the blockade is ineffective and thus may be permanent. Our findings show that neural activity and specifically the activation of postsynaptic cortical neurons has a prominent role in establishing the primary sensory map in S1, as well as the topographic organization of higher order synaptic connections.

OB protein binds specifically to the choroid plexus of mice and rats.

Binding studies were conducted to identify the anatomical location of brain target sites for OB protein, the ob gene product. 125I-labeled recombinant mouse OB protein or alkaline phosphatase-OB fusion proteins were used for in vitro and in vivo binding studies. Coronal brain sections or fresh tissue from lean, obese ob/ob, and obese db/db mice as well as lean and obese Zucker rats were probed to identify potential central OB protein-binding sites. We report here that recombinant OB protein binds specifically to the choroid plexus. The binding of OB protein (either radiolabeled or the alkaline phosphatase-OB fusion protein) and its displacement by unlabeled OB protein was similar in lean, obese ob/ob, and obese db/db mice as well as lean and obese Zucker rats. These findings suggest that OB protein binds with high affinity to a specific receptor in the choroid plexus. After binding to the choroid plexus receptor, OB protein may then be transported across the blood-brain barrier into the cerebrospinal fluid. Alternatively, binding of OB protein to a specific receptor in the choroid plexus may activate afferent neural inputs to the neural network that regulates feeding behavior and energy balance or may result in the clearance or degradation of OB protein. The identification of the choroid plexus as a brain binding site for OB protein will provide the basis for the construction of expression libraries and facilitate the rapid cloning of the choroid plexus OB receptor.

Blockade of action potential activity alters initial arborization of thalamic axons within cortical layer 4.

In the formation of connections during the development of the nervous system, it is generally accepted that there is an early phase not requiring neural activity and a later activity-dependent phase. The initial processes of axonal pathfinding and target selection are not thought to require neural activity, whereas the later fine-tuning of connections into their final adult patterns does. We report an apparent exception to this rule in which action potential activity seems to be required very early in development for thalamic axons to form appropriate patterns of terminal arborizations with their ultimate target neurons in layer 4 of the cerebral cortex. Blockade of sodium action potentials during the 2-week fetal period when visual thalamic axons initially grow into the primary visual cortex in cats prevents the normally occurring branching of lateral geniculate nucleus axons within layer 4. This observation implies a role for action-potential activity in cerebral cortical development far earlier than previously suspected, weeks before eye-opening and the onset of the well-known process of activity-dependent reorganization of axonal terminal arbors that leads to the formation of ocular dominance columns.