GM130 is a peripheral membrane protein strongly attached to the Golgi membrane and is isolated from the detergent and salt resistant Golgi matrix. GM130 is rich in coiled-coil structures and predicted to take a rod-like shape. Together with p115, giantin, and GRASP65, GM130 facilitates vesicle fusion to the Golgi membrane as a vesicle “tethering factor”. GM130 is also involved in the maintenance of the Golgi structure and plays a major role in the disassembly and reassembly of the Golgi apparatus during mitosis. Emerging evidence suggests that GM130 is involved in the control of glycosylation, cell cycle progression, and higher order cell functions such as cell polarization and directed cell migration. This creates the potential for novel Golgi-targeted drugs and treatments for various diseases including glycosylation defects, immune diseases, and cancer.
We have previously shown that chronic donepezil treatment induces nicotinic acetylcholine receptor up-regulation and enhances the sensitivity of the neurons to the neuroprotective effect of donepezil. Further analyses revealed that the nicotinic receptor is involved in this enhancement. In this study, we examined whether nicotinic receptor stimulation is sufficient to make neurons more sensitive to donepezil. We treated primary cultures of rat cortical neurons with nicotine and confirmed that chronic nicotine treatment induced nicotinic receptor up-regulation and made the neurons more sensitive to the neuroprotective effects of donepezil. Analyses with receptor antagonists and kinase inhibitors revealed that the effects of chronic nicotine treatment are mediated by nicotinic receptors and their downstream effectors including phosphatidylinositol 3-kinase. In contrast to chronic donepezil treatment that enhanced the level of nicotine-induced Ca2+ influx, chronic nicotine treatment did not significantly alter the level of Ca2+ influx.
Pharmacological properties were evaluated for the antidiarrheic wood creosote ingredient 2-methoxy-4-ethylphenol (2M4EP), which was shown to be protective against neurotoxicity of N-methyl-D-aspartate (NMDA), to modulate Ca2+ influx across acquired and native NMDA receptor (NMDAR) channels. NMDA markedly increased intracellular free Ca2+ levels in HEK293 cells transfected with the expression vector of either NR2A or NR2B subunit together with the essential NR1 subunit vector. Further addition of dizocilpine inhibited the increase by NMDA in intracellular Ca2+ levels in both types of acquired NMDAR channels, while 2M4EP and the NR2B-subunit–selective antagonist ifenprodil were more effective in inhibiting the increase by NMDA in HEK293 cells expressing NR1/NR2B subunits than in those with NR1/NR2A subunits. 2M4EP significantly prevented the increased intracellular Ca2+ levels by NMDA in cultured rat hippocampal neurons. Brief exposure to NMDA led to a drastic decrease in cellular viability 24 h later in cultured hippocampal neurons, while 2M4EP significantly prevented the loss of cellular vitality by NMDA. Similarly, 2M4EP more efficiently protected HEK293 cells with NR1/NR2B subunits than those with NR1/NR2A subunits. These results suggest that 2M4EP may protect neurons from excitotoxicity through inhibition of Ca2+ influx across NMDAR channels composed of NR1/NR2B, rather than NR1/NR2A, subunits.
The present study was undertaken to investigate changes of the electroencephalogram (EEG) induced by pentetrazol (PTZ) in comparison with behavioral seizures in mice. Under pentobarbital anesthesia, mice were fixed to a stereotaxic apparatus, and electrodes were implanted into the frontal and occipital cortex. Behavioral and EEG changes were observed for 30 min following PTZ administration. After PTZ administration, mice showed myoclonic seizure (MCL) and clonic seizure (CL) in order. At the same time, spiking activity and spike-wave discharge in the cortex were observed. Phenobarbital, sodium valproate, diazepam, ethosuximide, and gabapentin caused a dose-dependent shortening of the duration of MCL and CL. In addition, they shortened the duration of spiking activity and spike-wave discharge dose-dependently. Moreover, phenytoin significantly inhibited the duration of spiking activity. It can be concluded that PTZ-induced spiking activity and spike-wave discharge serve as useful indices to assess the potential of antiepileptic activity in absence and MCLs in humans. Moreover, it is supposed that employing an index of EEG activity in addition to that of behavioral activity is desirable for objectivity.
Inhibition of the vascular endothelial growth factor (VEGF) signaling pathway during pregnancy contributes to several pathologic pregnancies, such as hypertension, preeclampsia, and intrauterine growth restriction, but its effects on the fetus have not been fully examined. To determine how inhibition of the VEGF signaling pathway affects the fetal vascular development of mid pregnancy, we treated pregnant mice daily with either the VEGF receptor-2 (VEGFR-2) tyrosine kinase inhibitor KRN633 (300 mg/kg, p.o.) or the vehicle from 13.5 to 15.5 day of pregnancy. On the 16.5 day of pregnancy, the vascular beds in the placenta and several organs of the fetus were visualized by fluorescent immunohistochemistry. All mice treated with KRN633 appeared healthy, and total numbers of fetuses per litter were unaffected. However, weights of the placenta and fetus from KRN633-treated mice were lower than those from the vehicle-treated ones. No external malformations and bleeding were observed in the placenta and fetus, whereas immunohistochemical analyses revealed that the vascular development in labyrinthine zone of placenta and fetal organs examined (skin, pancreas, kidney, and lung) were impaired by KRN633 treatment. These results suggest that inhibition of the VEGF signaling pathway during mid pregnancy suppresses vascular growth of both the placenta and fetus without obvious health impairments of mother mice and increases the risk of induction of intrauterine growth restriction.
Ca2+-activated K+ (KCa) channels are important for endothelium-derived hyperpolarizing factor (EDHF) signaling. Since treatment with angiotensin II receptor blockers (ARBs) improves vasculopathies in type 2 diabetic patients, we asked whether the EDHF-type relaxation and its associated KCa channels [small (SKCa)–, intermediate (IKCa)–, and large (BKCa)–conductance channels] are abnormal in mesenteric arteries isolated from Goto-Kakizaki (GK) rats at the chronic stage of type 2 diabetes (34 – 38 weeks) and whether an ARBs (losartan, 25 mg · kg−1 · day−1 for 2 weeks) might correct these abnormalities. Although the acetylcholine chloride–induced EDHF-type relaxation in mesenteric arteries from GK rats was reduced versus the Wistar controls, it was significantly restored by losartan treatment. The SKCa-blocker apamin or the IKCa-blocker 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34) inhibited such relaxations in the losartan-treated or -untreated Wistar groups and in the losartan-treated GK group, but not in the losartan-untreated GK group. The BKCa-blocker iberiotoxin had a significant inhibitory effect in only one of these groups, the losartan-treated GK. The relaxations induced by the SKCa/IKCa activator NS309 and the BKCa activator NS1619, which were impaired in GK rats, were normalized by losartan treatment. We conclude that losartan improves EDHF-type relaxation in GK rats at least partly by normalizing SKCa/IKCa activities and increasing BKCa activity.
The L-type Ca2+ channel (CaV1.2) shows clear Ca2+-dependent facilitation and inactivation. Here we have examined the effects of calmodulin (CaM) and Ca2+ on Ca2+ channel in guinea-pig ventricular myocytes in the inside-out patch mode, where rundown of the channels was controlled. At a free [Ca2+] of 0.1 μM, CaM (0.15, 0.7, 1.4, 2.1, 3.5, and 7.0 μM) + ATP (2.4 mM) induced channel activities of 27%, 98%, 142%, 222%, 65%, and 20% relative to the control activity, respectively, showing a bell-shaped relationship. Similar results were observed at a free [Ca2+] <0.01 μM or with a Ca2+-insensitive mutant, CaM1234, suggesting that apoCaM may induce facilitation and inactivation of the channel activity. The bell-shaped curve of CaM was shifted to the lower concentration side with increasing [Ca2+]. A simple model for CaM- and Ca2+-dependent modulations of the channel activity, which involves two CaM-binding sites, was proposed. We suggest that both apoCaM and Ca2+/CaM can induce facilitation and inactivation of CaV1.2 Ca2+ channels and that the basic role of Ca2+ is to accelerate CaM-dependent facilitation and inactivation.
We have reported that the differentiation-inducing factors (DIFs) DIF-1 and DIF-3, morphogens secreted from Dictyostelium discoideum, inhibit proliferation of several cancer cells via suppression of the Wnt/β-catenin signaling pathway. However, the target molecules of DIFs involved in the anti-proliferative effects are still unknown. In the present study, DIF-1–tethered resins were synthesized to explore the target molecules of DIFs, and mitochondrial malate dehydrogenase (mMDH) was identified as one of the target molecules. In thein vitro assay, DIF-1 and other analogs including 2-MIDIF-1, DIF-3, and 6-MIDIF-3 were found to be capable of binding to mMDH but not to cytoplasmic MDH. However, only DIF-1 and 2-MIDIF-1 inhibited the enzymatic activity of mMDH. The effects of DIF analogs on ATP content and cell proliferation were then analyzed using HeLa cells. DIF-1 and 2-MIDIF-1 were found to lower the ATP content and both chemicals inhibited HeLa cell proliferation, suggesting that inhibition of mMDH activity affected cell energy production, probably leading to the inhibition of proliferation. These results suggest that the inhibition of mMDH activity by DIF-1 and 2-MIDIF-1 could be one of the mechanisms to induce anti-proliferative effects, independent of the inhibition of the Wnt/β-catenin signaling pathway.
Although a blockade of acetylcholine esterase has been reported to suppress neuronal cell death induced by exogenous glutamate and β-amyloid, information is still limited regarding the neuroprotective effects of the acetylcholine esterase inhibitor donepezil. We histologically examined the effects of donepezil on neuronal injury induced by ischemia–reperfusion. Intravenous and intravitreous treatment with donepezil 15 min prior to ischemia dramatically reduced the retinal damage. The protective effect of donepezil in the ganglion cell layer was not affected by mecamylamine, a nicotinic acetylcholine-receptor antagonist, nor scopolamine, a muscarinic acetylcholine-receptor antagonist. The protective effect of donepezil in the inner plexiform layer was reduced not by mecamylamine, but by scopolamine. Neostigmine, a choline-esterase inhibitor, and pilocarpine, a muscarinic acetylcholine-receptor agonist, have protective effects in the inner plexiform layer and the inner nuclear layer. These results suggest that not only the activation of acetylcholine receptors but also a mechanism unrelated to acetylcholine-esterase inhibition contribute to the protective effect of donepezil on the ganglion cells in the ischemic–reperfused rat retina. Donepezil may be useful as a therapeutic drug against retinal diseases that cause neuronal cell death such as glaucoma with high intraocular pressure.
We previously reported that acetylcholine (ACh)–induced vasodilation of retinal arterioles is diminished in diabetic rats; however, the underlying mechanism(s) of this phenomenon has not been fully elucidated. To determine the role of the polyol pathway in the diabetes-induced retinal vascular dysfunction, we investigated the effect of GP-1447, an inhibitor of aldose reductase, on the attenuation of ACh-induced vasodilation of retinal arterioles seen in diabetic rats. Male Wistar rats were treated with streptozotocin (STZ) and experiments were performed 2 weeks later. The STZ-treated animals were given drinking water containing 5% D-glucose to shorten the term for the development of retinal vascular dysfunction. Treatment with GP-1447 was initiated immediately after STZ treatment and continued throughout the 2-week experimental period. The attenuation of retinal vascular responses to ACh were not modified by treatment with GP-1447, whereas the aldose reductase inhibitor completely prevented diabetes-induced thinning of the retina and sorbitol accumulation in the retina and the lens. These results suggest that mechanisms that are independent of the polyol pathway may contribute to the onset of retinal endothelial dysfunction, although the pathway plays an important role in morphological changes of retina and formation of cataracts in diabetic rats.
Recently, an isomeric mixture of herbal anti-inflammatory naphthoquinones shikonin and alkannin, and their derivatives, have been found to impair cellular responses involving nitric oxide (NO) and NO synthesis, like the acetylcholine-induced relaxation response of rat thoracic aorta and NO release from murine RAW 264.7 macrophages. However, the mechanisms of such effects, including whether NO synthase (NOS) activity is affected, remained unclear. We herein investigate possible targets of shikonin in these NOS-related events. Shikonin by itself dose-dependently inhibited the rat thoracic aorta relaxation in response to acetylcholine (pD′2 value: 6.29). Its optical enantiomer, alkannin, was equally inhibitory in the aorta relaxation–response assay. In RAW 264.7 cells, shikonin inhibited the lipopolysaccharide-induced NO production by 82% at 1 μM. A cell-free assay to verify direct effects on NOS activity showed that shikonin inhibits all isoforms of NOS (IC50s, 4 – 7 μM), suggesting NOS as an inhibition target in both the events. Further possible targets of shikonin that might be involved in the inhibitions of the acetylcholine-induced aorta relaxation response and the NO generation by RAW 264.7 cells are also discussed. It is shown for the first time that shikonin inhibits NOS activity.
Glycine is an inhibitory neurotransmitter in the spinal dorsal horn and its extracellular concentration is regulated by glial glycine transporter (GlyT) 1 and neuronal GlyT2. This study was conducted to elucidate the effects of intrathecal injections of GlyT1 and GlyT2 inhibitors on two distinct types of mechanical allodynia, dynamic and static allodynia, in mice with herpetic or postherpetic pain. The GlyT2 inhibitor ALX1393, but not the GlyT1 inhibitor sarcosine, suppressed dynamic and static allodynia at the herpetic and postherpetic stages. Intrathecal ALX1393 suppressed dynamic allodynia induced by intrathecal strychnine and N-methyl-D-aspartate (NMDA). Intrathecal sarcosine suppressed dynamic allodynia induced by intrathecal strychnine, but not NMDA. Expression level of GlyT1, but not GlyT2, mRNA in the lumbar dorsal horn was decreased at the herpetic and postherpetic stages. Glycine receptor α1-subunit mRNA was decreased in the lumbar dorsal horn at the herpetic, but not postherpetic stage, without alteration in α3-subunit mRNA. The results suggest that GlyT2 is a potential target for treatment of dynamic and static allodynia in patients with herpes zoster and postherpetic neuralgia. The lack of efficacy of GlyT1 inhibitor may be explained by activation of NMDA receptors and the down-regulation of GlyT1 in the lumbar dorsal horn.
We investigated the enhancing effect of two metal-chelating compounds, 2,3-dimercapto-1-propanesulfonic acid (DMPS) and meso-2,3-dimercaptosuccinic acid (DMSA), on the antitumor activity of cisplatin (CDDP). In the in vivo experiments, DMPS showed a clear synergistic effect and significantly enhanced the antitumor activity of CDDP in terms of survival and life span in mice transplanted with ascites sarcoma 180 cells (S180 cells) at a dose of <100 μmol/kg, s.c., but not at a dose of >500 μmol/kg. On the other hand, DMSA did not enhance the antitumor activity of CDDP. DMPS (50 μmol/kg, s.c.) combined with CDDP also potently suppressed [3H]thymidine uptake in S180 cells implanted in mice, whereas DMSA did not. In the in vitro experiments, DMPS (10−6 to 10−5 M) produced a time- and dose-dependent decrease in intracellular Ca2+ concentrations ([Ca2+]i) in S180 cells and, in combination with CDDP, yielded a significant increase in intracellular platinum accumulation compared to that in cells treated with CDDP alone. These results indicate that DMPS used in combination with CDDP may be of considerable benefit in enhancing the cytotoxicity of CDDP in tumor cells, especially at a low dose. The results also suggest that the enhancing effect of DMPS is closely related to a decrease in [Ca2+]i and that the suitable dose and adequate administrational time of DMPS are important for its effective action.
Endocannabinoids have been shown to activate reward-related feeding and to promote astrocytic differentiation. We investigated whether high-fat diet (HFD) intake produced a preference for HFD via an endocannabinoid-dependent mechanism. In the conditioned place preference test, the 2-week HFD–intake group showed preference for HFD and had increased expression of a marker for reactive astrocytes, glial fibrillary acid protein (GFAP), in the hypothalamus. The cannabinoid CB1–receptor antagonist O-2050 reduced the preference for HFD and expression of GFAP in the hypothalamus. These results suggested that HFD intake led to the development of a preference for HFD via astrocytic CB1 receptors in the hypothalamus.
The rise of Ca2+ concentration ([Ca2+]i) by reducing external Na+ in urinary bladder smooth muscle cells (UBSMCs) from transgenic mice overexpressing Na+/Ca2+ exchanger type-1.3 (NCX1.3tg/tg) was about 4 times as large as that in the wild-type (WT). NCX1 protein expression in UB increased about 4-fold in NCX1.3tg/tg. The Ca2+ release by caffeine in UBSMCs was comparable between NCX1.3tg/tg and WT, but [Ca2+]i decay was faster in NCX1.3tg/tg. Contractions induced by acetylcholine, 60 mM K+, or electrical stimulation were significantly smaller in UB segments of NCX1.3tg/tg. NCX worked in Ca2+-extrusion mode during these contractions in UBSMCs of both WT and NCX1.3tg/tg.
We compared mechanical responses to uridine-5′triphosphate (UTP) and 2-(methylthio)adenosine-5′diphosphate (2MeSADP) of cerebral arteries isolated from dogs and monkeys. In the dog, UTP induced endothelium-independent contraction, whereas 2MeSADP induced endothelium-dependent relaxation that was abolished by NG-nitro-L-arginine (L-NA). In the monkey, both UTP and 2MeSADP induced endothelium-dependent relaxation. L-NA largely inhibited the UTP-induced relaxation whereas it partially inhibited the 2MeSADP-induced relaxation, and both remaining relaxations were abolished by charybdotoxin plus apamin. In conclusion, dog and monkey cerebral arteries respond differentially to UTP and similarly to 2MeSADP; however, involvement of endothelium-derived relaxing factor in the endothelium-dependent relaxation by 2MeSADP is quite different between the two species.