GABAA receptors are heteropentameric ligand-gated chloride channels composed of a variety of subunits, including α1 – 6, β1 – 3, γ1 – 3, δ, ε, θ, and π, and play a key role in controlling inhibitory neuronal activity. Modification of the efficacy of the synaptic strength is produced by changes in both the number of neuronal surface receptors and pentameric molecular assembly, leading to differences of sensitivity to neurotransmitters and neuromimetic drugs. Therefore, it is important to understand the molecular mechanisms regulating the so-called “life cycle of GABAA receptors” including sequential pentameric assembly at the site synthesized, intracellular transport through the Golgi apparatus and the cytoplasm, insertion into the cell membrane, functional modulation at the cell surface, and finally internalization, followed by either recycling back to the surface membrane or lysosomal degradation. This review is focused on events related to the surface expression of the receptor containing the γ2 subunit and clathrin/AP2 complex–mediated phospho-regulated endocytosis of the receptor, with special reference to the function of novel GABAA receptor modulators, GABARAP (GABAA receptor-associated protein) and PRIP (phospholipase C-related, but catalytically inactive protein).
The cell signaling cascades provoked by Wnt proteins (the Wnt signaling pathways), which are well conserved through evolution, play crucial roles to maintain homeostasis of a variety of tissues such as skin, blood, intestine, and brain, as well as to regulate proliferation, morphology, motility, and fate of cells during embryonic development. Among these pathways, the signal transduction through β-catenin (the Wnt/β-catenin signaling pathway) has been most intensively studied because this signal regulates the expression of a number of genes essential for cell proliferation and differentiation and also this pathway is perturbed in a number of diseases such as cancers, bone diseases, and cardiovascular diseases. However, there is no therapeutic agents that can selectively modulate the Wnt/β-catenin signaling pathway, although some existing drugs (e.g., non-steroidal anti-inflammatory drugs, vitamins, and imatinib mesylate) have been suggested to inhibit this pathway. Here we provide an overview of the Wnt/β-catenin signaling pathway: its roles in physiology and pathology and the possibility as a target in development of new drugs.
The effect of Daikenchuto, a traditional herbal medicine, on gastrointestinal hypoperistalsis in postoperative ileus (POI) was investigated. POI was induced by laparotomy with manipulation of the gastrointestine under anesthesia, and gastrointestinal transit was calculated by migration of Evans blue. Daikenchuto (270 – 2,700 mg/kg, p.o.) dose-dependently improved the delayed gastrointestinal transit in POI. This effect of Daikenchuto was partially inhibited by SB204070 (1 mg/kg, s.c.), a 5-hydroxytriptamine4 (5-HT4)-receptor antagonist and completely abolished by atropine (1 mg/kg, s.c.), a muscarine-receptor antagonist. Among the constituents of Daikenchuto, the medical herb zanthoxylum fruit (60 mg/kg, p.o.) and maltose syrup (2,400 mg/kg, p.o.) significantly ameliorated the delayed gastrointestinal transit, but ginseng and processed ginger did not affect the gastrointestinal transit in the rat POI. The improvement induced by zanthoxylum fruit was also inhibited by atropine or SB204070. In addition, the high osmotic pressure of the maltose syrup (2400 mg/10 mL per kg) was related to the improvement of delayed gastrointestinal transit. These results demonstrated that Daikenchuto ameliorates postoperative hypoperistalsis via cholinergic nerves and 5-HT4 receptors and that osmotic pressure also may be involved in this action. Moreover, zanthoxylum fruit and maltose syrup were crucial medical herbs contributing to the ability of Daikenchuto.
The mechanism by which ibudilast induces vasodilation was examined in isolated endothelium-denuded rat aorta. Ibudilast inhibited the contractions induced by phenylephrine (PE) and high K+ with decrease of [Ca2+]i level in a concentration-dependent manner, to the same degree. 3-Isobutyl-1-methylxanthine (IBMX) inhibited PE-induced contraction and [Ca2+]i level in a concentration-dependent manner, but it inhibited high K+-induced contraction without decrease of [Ca2+]i level. In comparison with IBMX, the increases of cAMP and cGMP contents in ibudilast were much smaller than that of muscle tension. Ibudilast did not inhibit 12-deoxyphorbol 13-isobutyrate (DPB)-induced contraction in the presence of verapamil. Treatment with 30 μM ibudilast inhibited the extracellularly added Ca2+-induced muscle tension and increases in [Ca2+]i level during high K+ depolarization. These results suggested that ibudilast inhibited PE- and high K+-induced muscle contractions mainly by the inhibition of [Ca2+]i level in endothelium-denuded rat aorta.
Nω-Nitro-L-arginine methyl ester (L-NAME) induces a pre-eclampsia-like syndrome in pregnant rats. We have previously reported the anti-hypertensive effects of several Japanese traditional (Kampo) medicines in this model, and one of these, Tokishakuyakusan (TS), also improved intrauterine growth retardation (IUGR). In the present study, we characterized the effect of TS on IUGR. TS administration reversed the decrease in fetal body weight and fetal blood glucose concentration induced by the infusion of L-NAME. Growth hormone (GH) levels in the fetal blood, which were decreased by L-NAME infusion, were also significantly elevated by TS; however, levels of GH releasing hormone (GHRH) and insulin-like growth factor I (IGF-I) were unchanged and only slightly changed, respectively. Treatment with L-NAME with or without TS had no apparent effect on GH, GHRH, and IGF-I levels of dams. In an immunocytochemical study, the number of GH-positive cells in the fetal pituitary gland was significantly increased in TS-treated rats. These data suggest that enhanced proliferation of somatotrope cells of the pituitary gland and the resultant increase in GH secretion in the fetus may be involved in the improvement of IUGR by TS.
In order to determine the differential effects of flavonoids on cerebral ischemia, we investigated the effects of (−)-epigallocatechin gallate (EGCG), catechin, rutin, and quercetin on spatial memory impairment and neuronal death induced by repeated cerebral ischemia in rats. Both rutin and quercetin (50 mg/kg × 2) improved spatial memory impairment in the 8-arm radial maze task and neuronal death in the hippocampal CA1 area; however, catechin (200 mg/kg × 2) and EGCG (50 mg/kg × 1) did not. Administration of EGCG (50 mg/kg × 2) resulted in a high mortality rate. These results suggest that in this repeated cerebral ischemia model, the 4-oxo group and the 2,3-double bond in the C ring of rutin and quercetin are related to their neuroprotective action.
We have previously demonstrated that the antiepileptic drug zonisamide supraspinally generates analgesic effects on thermal and mechanical hypersensitivity in mice after peripheral nerve injury. To further establish the neurochemical basis for the supraspinally mediated analgesic action of zonisamide, we measured spinal noradrenaline (NA), 3-methoxy-4-hydroxyphenyleneglycol (MHPG), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and dopamine (DA) contents using HPLC with electrochemical detection in a murine neuropathic pain model that was prepared by partial ligation of the sciatic nerve (Seltzer model). Intraperitoneally or intracerebroventricularly administered zonisamide (50 mg/kg, i.p. and 30 μg, i.c.v., respectively), which almost completely reduced mechanical hypersensitivity, did not elicit any changes in spinal NA, MHPG, 5-HT, 5-HIAA, and DA contents. Moreover, the effectiveness of i.p. or i.c.v. administered zonisamide at reducing thermal and mechanical hypersensitivity was not influenced by intrathecally administered yohimbine (3 μg), an α2-adrenergic receptor antagonist. Thus, it appears that the supraspinally mediated analgesic effects of zonisamide are independent of the descending monoaminergic pain inhibitory system.
We examined whether edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one), a free radical scavenger, exerts its protective effect on coronary microvessels after ischemia/reperfusion (I/R) in vivo. Ninety-minute coronary occlusion followed by reperfusion was performed in 16 open-chest dogs with and without edaravone administration. Coronary small artery (≥100 μm in size) and arteriolar (<100 μm) vasodilation, in the presence of endothelium-dependent (acetylcholine) or -independent (papaverine) vasodilators, was directly observed using intravital microscopy before and after I/R. I/R impaired microvascular vasodilation in response to acetylcholine, whereas administration of edaravone preserved the response in microvessels of both sizes, but to a greater extent in the coronary small arteries. No significant changes were noted with papaverine administration. In the edaravone group, the fluorescent intensity from reactive oxygen species (ROS) was lower, whereas nitric oxide (NO) intensity was higher relative to controls in the microvessels of the ischemic area. In conclusion, edaravone preserves coronary microvascular endothelial function after I/R in vivo. These effects, which were NO-mediated, were attributed to the ROS scavenging properties of edaravone.
Donepezil is a potent and selective acetylcholinesterase inhibitor developed for the treatment of Alzheimer’s disease. To elucidate whether donepezil causes neuronal differentiation, we examined its effect on nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells. Donepezil (10 μM) significantly potentiated the neurite outgrowth evoked by low (1 ng/ml) and high (50 ng/ml) concentrations of NGF. The effect of donepezil (1 – 10 μM) was concentration-dependent. The enhancement of neurite outgrowth caused by donepezil was not blocked by the acetylcholine receptor (AChR) antagonists mecamylamine and scopolamine. Furthermore, the AChR agonists nicotine and carbachol did not affect the neurite outgrowth induced by NGF. Donepezil (10 μM) also significantly potentiated neurite outgrowth evoked by dibutyryl cyclic AMP. Moreover, donepezil potentiated the NGF-induced phosphorylation of extracellular signal-regulated kinase (ERK). These results suggest that donepezil potentiated neuronal differentiation by enhancing the activation of ERK.
The effect of wogonin, a flavone highly purified from the roots of Scutellaria baicalensis, on apoptotic cell death was re-evaluated in rat thymocytes. This flavone inhibited glucocorticoid-induced apoptotic changes such as DNA fragmentation, phosphatidylserine translocation, and nuclear condensation in rat thymocytes. Similar inhibition was also observed in apoptosis induced by other inducers such as etoposide. No significant changes of these apoptotic features were observed in rat thymocytes treated with wogonin alone, suggesting that this flavone protects against glucocorticoid-mediated immunosuppression caused by thymocyte apoptosis. Wogonin was reported to possess anti-inflammatory action in some previous studies, but this flavone had no effect on carrageenan-induced paw edema in this study. The simultaneous treatment of wogonin and glucocorticoid neither enhanced nor reduced the anti-inflammatory effect of glucocorticoid. These results indicate that wogonin is likely to prevent the immunosuppression of glucocorticoid without diminishing its drug efficacy as an anti-inflammatory agent.
Bovine lactoferrin (bLf) is an iron-binding secretory protein present in breast milk, mucosal secretions, and the secondary granules of neutrophils. Although bLf has multiple functions, including antimicrobial and immunomodulatory activities, its effect on neuronal cells is not fully understood. We report that bLf prevents cell adhesion of PC12 cells and allows them to be cultivated in suspension. PC12 cells normally adhere well to plastic culture plates and show anchorage-dependent cell growth, but we found that soon after adding bLf, they detach from culture plates and begin to grow in suspension. When bLf was removed from the medium, the cells began to re-adhere to the plates. Thus, bLf inhibits cell adhesion and stimulates anchorage-independent growth in PC12 cells. On the other hand, bLf-induced cell suspension growth was not observed when cells were grown on a laminin matrix, suggesting that bLf does not affect integrin-mediated cell adhesion on a laminin matrix. Treatment of cells with heparin or chondroitin sulfate A or C inhibited bLf-induced growth in cell suspension. Furthermore, pretreatment of cells with heparinase and/or chondroitinase prevented direct binding of bLf to the cell membrane. These results suggest that bLf binds to the membrane of PC12 cells via membrane-associated proteoglycans and leads to anchorage-independent growth.
Compounds such as S-allylmercaptocysteine, diallyl disulfide, and S-trityl-L-cysteine isolated from garlic have been known to be effective in chemoprevention. Nuclear transcription factor-κB (NF-κB) has been known to be an implicated factor in apoptotic cell death of several cancer cells. In this study, we investigated whether a sulfurcompound (named thiacremonone) isolated from garlic could modulate NF-κB activity and thereby induce apoptotic cell death of colon cancer cells. Treatment with different concentrations (30 – 150 μg/ml) of thiacremonone for various periods (0 – 48 h) inhibited colon cancer cell (SW620 and HCT116) growth followed by induction of apoptosis in a dose-dependent manner. We also found that thiacremonone modulated tumor necrosis factor-α (TNF-α) and tetradeanoyl phorbol acetate (TPA)-induced NF-κB transcriptional and DNA binding activity. Moreover, thiacremonone suppressed NF-κB target anti-apoptotic genes (Bcl-2, cIAP1/2, and XIAP) and inflammatory genes (iNOS and COX-2), whereas it induced apoptotic genes (Bax, cleaved caspse-3, and cleaved PARP) expression. These results suggest that a novel sulfurocompound from garlic inhibited colon cancer cell growth through induction of apoptotic cell death by modulating of NF-κB.
Simvastatin, a cholesterol synthesis inhibitor, enhances BMP2 expression in osteoblasts. The purpose of the present study was to examine whether simvastatin stimulates bone regeneration when combined with calcium sulfate as a carrier. Critical-sized bone defects in rat calvaria were treated with calcium sulfate or with combination of 1 mg simvastatin and calcium sulfate. In the combination group, although the least amount of bone formation with intense soft tissue inflammation was observed at 2 and 4 weeks, remarkable bone formation was evident at 8 weeks. Conclusively, the combination of simvastatin and calcium sulfate stimulated bone regeneration in spite of the inflammatory response.
Although primary cultures of neurons are essential methods for cell biological and pharmacological researches, many animals must be sacrificed for each experiment. Here we introduce a novel system to cryopreserve hippocampal granule cells (GCs) prepared from postnatal rats. Being thawed after as long as 60 days of cryopreservation, GCs expressed the mature neuronal marker MAP-2 and elongated single tau-1-positive axons and multiple tau-1-negative dendrites. These properties closely resembled intact GCs in primary cultures, providing the advantage of being able to repeatedly prepare stable cultures with a single sacrifice of animals.
We investigated the effects of NaHS, a hydrogen sulfide (H2S) donor, on the tension of isolated mouse and guinea-pig bronchial rings. NaHS at 0.01 – 10 mM had no effect on the tone of those preparations without precontraction. When the preparation was precontracted with carbachol, NaHS at 0.1 – 3 mM strongly relaxed the mouse rings, but produced only slight relaxation in the guinea-pig rings. The NaHS-induced relaxation in the mouse bronchus was resistant to inhibitors of ATP-sensitive K+ channels, soluble guanylyl cyclase, cyclooxygenase (COX)-1 or COX-2, and antagonists of tachykinin receptors. Thus, NaHS evokes bronchodilation in mice, suggesting a possible role for H2S in the respiratory system.
We examined the source of Ca2+ involved in the volume regulation of Madin-Darby canine kidney (MDCK) cells with confocal microscopy and fluoroprobes. Hyposmosis induced a transient increase in cell volume, as well as cytoplasmic Ca2+, which peaked at 3 to 5 min and gradually decreased to reach the initial value within about 30 min. This late decrease in cell volume, as well as the transient rise in cytoplasmic Ca2+, was reduced in Ca2+-free solution and was abolished by pretreatment with thapsigargin. In conclusion, Ca2+ released from the intracellular store contributes to the regulatory volume decrease following hyposmotic swelling in MDCK cells.
We examined endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation of mesenteric arteries in high-sodium loaded streptozotocin (STZ)-induced diabetic rats. The study shows that acetylcholine (ACh)-induced, EDHF-mediated relaxation is relatively maintained in STZ-induced diabetic rats, but after a high-sodium diet was given, the function was significantly impaired in STZ-induced diabetic rats.