Tadashi Kusama

Targeting Phosphoinositide-3-Kinase-δ with Theophylline Reverses Corticosteroid Insensitivity in Chronic Obstructive Pulmonary Disease

RATIONALE Patients with chronic obstructive pulmonary disease (COPD) show a poor response to corticosteroids. This has been linked to a reduction of histone deacetylase-2 as a result of oxidative stress and is reversed by theophylline. OBJECTIVES To determine the role of phosphoinositide-3-kinase-delta (PI3K-δ) on the development of corticosteroid insensitivity in COPD and under oxidative stress, and as a target for theophylline. METHODS Corticosteroid sensitivity was determined as the 50% inhibitory concentration of dexamethasone on tumor necrosis factor-α-induced interleukin-8 release in peripheral blood mononuclear cells from patients with COPD (n = 17) and compared with that of nonsmoking (n = 8) and smoking (n = 7) control subjects. The effect of theophylline and a selective PI3K-δ inhibitor (IC87114) on restoration of corticosteroid sensitivity was confirmed in cigarette smoke-exposed mice. MEASUREMENTS AND MAIN RESULTS Peripheral blood mononuclear cells of COPD (50% inhibitory concentration of dexamethasone: 156.8 ± 32.6 nM) were less corticosteroid sensitive than those of nonsmoking (41.2 ± 10.5 nM; P = 0.018) and smoking control subjects (47.5 ± 19.6 nM; P = 0.031). Corticosteroid insensitivity and reduced histone deacetylase-2 activity after oxidative stress were reversed by a non-selective PI3K inhibitor (LY294002) and low concentrations of theophylline. Theophylline was a potent selective inhibitor of oxidant-activated PI3K-δ, which was up-regulated in peripheral lung tissue of patients with COPD. Furthermore, cells with knock-down of PI3K-δ failed to develop corticosteroid insensitivity with oxidative stress. Both theophylline and IC87114, combined with dexamethasone, inhibited corticosteroid-insensitive lung inflammation in cigarette-smoke-exposed mice in vivo. CONCLUSIONS Inhibition of oxidative stress dependent PI3K-δ activation by a selective inhibitor or theophylline provides a novel approach to reversing corticosteroid insensitivity in COPD.

Polyamine transport, accumulation, and release in brain.

Cycling of polyamines (spermine and spermidine) in the brain was examined by measuring polyamine transport in synaptic vesicles, synaptosomes and glial cells, and the release of spermine from hippocampal slices. It was found that membrane potential‐dependent polyamine transport systems exist in synaptosomes and glial cells, and a proton gradient‐dependent polyamine transport system exists in synaptic vesicles. The glial cell transporter had high affinities for both spermine and spermidine, whereas the transporters in synaptosomes and synaptic vesicles had a much higher affinity for spermine than for spermidine. Polyamine transport by synaptosomes was inhibited by putrescine, agmatine, histidine, and histamine. Transport by glial cells was also inhibited by these four compounds and additionally by norepinephrine. On the other hand, polyamine transport by synaptic vesicles was inhibited only by putrescine and histamine. These results suggest that the polyamine transporters present in glial cells, neurons, and synaptic vesicles each have different properties and are, presumably, different molecular entities. Spermine was found to be accumulated in synaptic vesicles and was released from rat hippocampal slices by depolarization using a high concentration of KCl. Polyamines, in particular spermine, may function as neuromodulators in the brain.

Mutagenesis of the GABA rho 1 receptor alters agonist affinity and channel gating.

Seventeen site-directed mutations were constructed in the GABA rho 1 receptor with the aim of finding agonist binding domains common to rho 1 and rho 2 receptors but distinct from those identified in members of the family of homologous, ligand gated ion channels. Mutated cDNAs were expressed in Xenopus oocytes and tested by voltage clamp experiments. Five of the mutations abolished responsiveness to GABA. Mutation Q189H, in the conserved cysteine loop, diminished apparent GABA affinity to about 1/10 of wild type values in a manner consistent with decreased allosteric cooperativity among agonist recognition sites. Mutation R316A, located in the extracellular loop between transmembrane domains II and III, increased the Hill coefficient to 3.9 in a fashion consistent with enhanced open probability of a receptor multimer.

Toll-like Receptor 3 Stimulation Causes Corticosteroid-Refractory Airway Neutrophilia and Hyperresponsiveness in Mice

BACKGROUND RNA virus infections, such as rhinovirus and respiratory syncytial virus, induce exacerbations in patients with COPD and asthma, and the inflammation is corticosteroid refractory. The main aim of this study is to establish a murine model induced by a Toll-like receptor 3 (TLR3) agonist, an RNA virus mimic, and investigate the response to corticosteroid. METHODS A/J mice were given polyinosinic-polycytidylic acid (poly[I:C]), a TLR3 agonist, intranasally, in the presence or absence of cigarette smoke exposure. Inflammatory cell accumulation and C-X-C motif chemokine (CXCL) 1, interferon (IFN), and CXCL10 production in BAL fluid (BALF) were determined by flow cytometry and enzyme-linked immunosorbent assay, respectively, and airway hyperresponsiveness (AHR) to histamine/methacholine was determined by a two-chambered, double-flow plethysmography system. BALB/c and C57BL/6J mice were also used for comparisons. RESULTS Intranasal treatment of poly(I:C) significantly induced airway neutrophilia; production of CXCL1, IFN-β, and CXCL10; and necrotic cell accumulation in BALF. It also increased airway responsiveness to histamine or methacholine inhalation. This poly(I:C)-dependent airway inflammation and AHR was not inhibited by the corticosteroid fluticasone propionate (FP) (up to 0.5 mg/mL intranasal), although FP strongly inhibited lipopolysaccharide (TLR4 agonist)-induced airway neutrophilia. Furthermore, cigarette smoke exposure significantly increased TLR3 expression in murine lung tissue and exacerbated poly(I:C)-induced neutrophilia and AHR. CONCLUSIONS These results suggest that TLR3 stimulation is involved in corticosteroid-refractory airway inflammation in lung, which is enhanced by cigarette smoking, and this may provide a model for understanding virus-induced exacerbations in COPD and their therapy.

Proliferative effects of angiotensin II and endothelin-1 on guinea pig gingival fibroblast cells in culture.

We investigated whether phenytoin (PHT) and nifedipine (NIF) induce angiotensin II (Ang II) and endothelin-1 (ET-1) generation by cultured gingival fibroblasts derived from guinea pigs and whether Ang II and ET-1 induce proliferation of these cells. Immunohistochemical experiments showed that PHT (250 nM) and NIF (250 nM) increased the immunostaining intensities of immunoreactive Ang II and ET-1 (IRET-1) in these cells. Captopril (3 microM), an angiotensin-converting enzyme inhibitor, reduced these enhanced intensities to control levels. Ang II (100 nM) enhanced the immunostaining intensity of IRET-1. PHT (250 nM) and NIF (250 nM)-induced cell proliferation. Both PHT- and NIF-induced proliferation was inhibited by captopril (3 microM). Ang II (100 nM) and ET-1 (100 nM) also induced cell proliferation. Ang II-induced proliferation was inhibited by CV11974 (1 microM), an AT(1) receptor antagonist and saralasin (1 microM), an AT(1)/AT(2) receptor antagonist, but not by PD123,319 (1 microM), an AT(2) receptor antagonist. ET-1-induced proliferation was inhibited by BQ123 (10 microM), an ET(A) receptor antagonist, but not by BQ788 (1 microM), an ET(B) receptor antagonist. These findings suggest that PHT- and NIF-induced gingival fibroblast proliferation is mediated indirectly through the induction of Ang II and ET-1 and probably mediated through AT(1) and ET(A) receptors present in or on gingival fibroblasts.

Monoamines directly inhibit N-methyl-d-aspartate receptors expressed in Xenopus oocytes in a voltage-dependent manner

Dopamine has numerous functions in the brain and has been shown to modulate responses of N-methyl-D-aspartate (NMDA) receptors on thalamic and hippocampus neurons [N.G. Castro, M.C.F. de Mello, F.G. de Mello, Y. Aracava, Direct inhibition of the N-methyl-D-aspartate receptor channel by dopamine and (+)-SKF38393, Br. J. Pharmacol. 126 (1999) 1847-1855]. Thus, the effects of dopamine, serotonin, tyramine, epinephrine, norepinephrine, and octopamine on NMDA receptors were studied using voltage-clamp recording of recombinant NMDA receptors expressed in Xenopus oocytes. Serotonin and tyramine, in addition to dopamine, were found to inhibit macroscopic currents at heteromeric NMDA receptors, but not AMPA (GluR1/GluR2) receptors. Epinephrine, norepinephrine and octopamine also weakly inhibited macroscopic currents at NR1/NR2A and NR1/NR2B receptors. The inhibitory effects of these monoamines became prominent at -100 mV comparing those at -20 mV. Mutations at NR1 N616, NR2B N615, and NR2B N616, but not at NR1 W563 and NR1 N650, reduced the inhibitory effects by monoamines. These results indicate that these monoamines directly act on the narrowest region of channel pore.

Effects of endothelin-1 and nitric oxide on proliferation of cultured guinea pig bronchial smooth muscle cells

The proliferative effects of endothelin-1 (ET-1), both alone and in combination with epidermal growth factor (EGF), and the effect of nitric oxide (NO) on the cell proliferation were investigated in cultured guinea pig bronchial smooth muscle cells. ET-1 (10-100 nM) alone augmented cell proliferation, and was additive to the effect of EGF (0.48 nM) in a concentration-dependent manner. An ET(A) antagonist, BQ-123 (10 microM), reduced the cell-proliferative effect of ET-1, whereas an ET(B) antagonist, BQ-788 (10 microM), did not influence the effect. A NO donor, SIN-1 (10 nM-1 microM), reduced the cell-proliferative effect of ET-1 in a concentration-dependent manner. The effect of SIN-1 (1 microM) was partly, but significantly, reversed by a soluble guanylyl cyclase inhibitor, ODQ (1 microM). These results suggest that ET-1 acts not only as a co-mitogen with EGF but also as a mitogen alone, and that its action is mediated through activation of ET(A) receptors. Therefore, ET-1 may contribute to airway remodeling, a pathophysiological hallmark of asthma. In addition, NO, which is produced mainly in the airway epithelium and is partly mediated through cGMP-dependent pathway, may reduce the phenomenon.

Consensus phosphorylation sites of human GABAC/GABAρ receptors are not critical for inhibition by protein kinase C activation

The mechanism of inhibition of human GABA(C)/GABArho receptors by protein kinase C (PKC) activation was investigated in Xenopus oocytes. Phorbol 12-myristate 13 acetate (PMA), a potent PKC activator, at 25 nM inhibited the currents through GABArho2 receptors, which have one consensus phosphorylation site by PKC in the predicted intracellular loops. The time-courses and amplitudes of inhibition were not significantly different from those occurring through GABArho1 receptors, which have six such sites. The inhibitory effect of PMA was also observed after removing each consensus phosphorylation site in both GABArho1 and rho2 receptors by site-directed mutagenesis. These results suggest that phosphorylation of consensus sites in the intracellular loops is not involved in the inhibition of human GABA(C)/GABArho receptors by PKC activation.

Sulfur amino acids deficiency caused by grass pea diet plays an important role in the toxicity of L-β-ODAP by increasing the oxidative stress: studies on a motor neuron cell line.

Neurolathyrism is a motor neuron disease caused by the overconsumption of grass pea (Lathyrus sativus L.) containing L-β-ODAP. The precise mechanism to cause motor neuron degeneration has yet to be elucidated, but should agree with the epidemiological backgrounds. Considering the amino acid content of the legume, and the epidemiological link with prolonged unbalanced nutrition, the shortage of sulfur amino acids methionine and cysteine could affect the toxicity of L-β-ODAP. We analyzed the effect of these amino acids in the media on the toxicity using primary motor neuron culture and a motor neuron cell line NSC-34. Deprivation of both methionine and cysteine exacerbated the toxicity of L-β-ODAP by 66% compared to the complete medium. The glutathione content of these cells was greatly decreased in sulfur amino acid-deprived medium. L-β-ODAP further lowered the content in the deprived media to be 32-44% of the controls compared to normal media being 62-74%. The increased motor neuron toxicity in this medium was neutralized by the addition of reduced glutathione ethyl ester or N-acetylcysteine suggesting the importance of the mitochondrial oxidative stress induced by L-β-ODAP under sulfur amino acid-deficient conditions.

Cyclophane and acyclic cyclophane: Novel channel blockers of N-methyl-d-aspartate receptor

The effects of cyclophanes (CPCn, CPPy and TGDMAP) and acyclic cyclophane (ATGDMAP) on various glutamate receptors were studied with these receptors expressed in Xenopus oocytes using voltage-clamp recording. CPCn, CPPy, TGDMAP and ATGDMAP were found to inhibit macroscopic currents at heteromeric NMDA receptors (NR1/NR2), but not Ca(2+)-permeable AMPA receptors (GluR1), Ca(2+)-nonpermeable AMPA receptors (GluR1/GluR2) and metabotropic glutamate receptors (mGluR1alpha). The inhibition of NR1/NR2A receptors by these compounds was more potent than those of the other NMDA receptor subtypes. At a resting potential (-70 mV), the IC(50) values of CPCn, CPPy, TGDMAP and ATGDMAP for NR1/NR2A receptors were 0.5+/-0.1, 1.0+/-0.2, 8.0+/-0.8 and 4.9+/-0.5 microM, respectively. The inhibition by these compounds was voltage-dependent, that is, the degree of inhibition was in the order of negative holding potentials, -100 mV>-70 mV>-20 mV. Results of experiments using mutant NR1 and NR2 subunits identified residues that influence block by CPCn. The inhibition by CPCn was not altered significantly in the mutants at the critical asparagines in the M2 loop, NR1 N616, NR2B N615 and NR2B N616, these residues are known to form the narrowest region of the channel and the binding site of Mg(2+). However, mutations at NR1 N650, located in the vestibule of channel pore, and NR1 D669, located in the extracellular region, reduced the inhibition by CPCn, suggesting that these amino acid residues interact with CPCn. These results suggest that CPCn interacts directly with the mouth or vestibule of the ion channel, like a lid.