[Show abstract][Hide abstract] ABSTRACT: Coumarin and its derivatives are fragrant natural compounds isolated from the genus Murraya that are flowering plants widely distributed in East Asia, Australia and the Pacific Islands. Murraya plants have been widely used as medicinal herbs for relief of pains such as headache, rheumatic pain, toothache and snake bites. However, little is known about their analgesic components and the molecular mechanism underlying pain relief. Here, we report the bioassay-guided fractionation and identification of a novel coumarin derivative, named muralatin L, that can specifically activate the nociceptor transient receptor potential vanilloid 1 (TRPV1) channel and reverse the inflammatory pain in mice through channel desensitization. Muralatin L was identified from active extract of M. alata against TRPV1 transiently expressed in HEK-293T cells in fluorescent calcium FlexStation assay. Activation of TRPV1 current by muralatin L and its selectivity were further confirmed by whole-cell patch clamp recordings of TRPV1 expressing HEK-293T cells and dorsal root ganglion neurons isolated from mice. Furthermore, muralatin L could reverse inflammatory pain induced by formalin and acetic acid in mice, but not in TRPV1 knockout mice. Taken together, our findings show that muralatin L specifically activates TRPV1 and reverses inflammatory pain, thus highlighting the potential of coumarin derivatives from Murraya plants for pharmaceutical and medicinal applications such as pain therapy.
Preview · Article · Oct 2015 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: The capsaicin receptor TRPV1 ion channel is a polymodal nociceptor that responds to heat with exquisite sensitivity through an unknown mechanism. Here we report the identification of a novel toxin, RhTx, from the venom of the Chinese red-headed centipede that potently activates TRPV1 to produce excruciating pain. RhTx is a 27-amino-acid small peptide that forms a compact polarized molecule with very rapid binding kinetics and high affinity for TRPV1. We show that RhTx targets the channel's heat activation machinery to cause powerful heat activation at body temperature. The RhTx–TRPV1 interaction is mediated by the toxin's highly charged C terminus, which associates tightly to the charge-rich outer pore region of the channel where it can directly interact with the pore helix and turret. These findings demonstrate that RhTx binding to the outer pore can induce TRPV1 heat activation, therefore providing crucial new structural information on the heat activation machinery.
[Show abstract][Hide abstract] ABSTRACT: Lung cancer or pulmonary carcinoma is primarily derived from epithelial cells that are thin and line on the alveolar surfaces of the lung for gas exchange. ANO1/TMEM16A, initially identified from airway epithelial cells, is a member of Ca2+-activated Cl- channels (CaCCs) that function to regulate epithelial secretion and cell volume for maintenance of ion and tissue homeostasis. ANO1/TMEM16A has recently been shown to be highly expressed in several epithelium originated carcinomas. However, the role of ANO1 in lung cancer remains unknown. In this study, we show that inhibition of calcium-activated chloride channel ANO1/TMEM16A suppresses tumor growth and invasion in human lung cancer. ANO1 is upregulated in different human lung cancer cell lines. Knocking-down ANO1 by small hairpin RNAs inhibited proliferation, migration and invasion of GLC82 and NCI-H520 cancel cells evaluated by CCK-8, would-healing, transwell and 3D soft agar assays. ANO1 protein is overexpressed in 77.3% cases of human lung adenocarcinoma tissues detected by immunohistochemistry. Furthermore, the tumor growth in nude mice implanted with GLC82 cells was significantly suppressed by ANO1 silencing. Taken together, our findings provide evidence that ANO1 overexpression contributes to tumor growth and invasion of lung cancer; and suppressing ANO1 overexpression may have therapeutic potential in lung cancer therapy.
[Show abstract][Hide abstract] ABSTRACT: The effect of acrylic acid additive on the electric conductivity of amorphous SiCN derived from polymeric precursor was studied. The conductivity showed to follow Arrhenius dependence on pyrolysis temperature, but with much smaller activation energy, as compared to the unmodified SiCN. Structural analysis using Raman and XPS revealed that the size of the free-carbon clusters within the AC-modified SiCN changed with pyrolysis temperature, but the sp2-to-sp3 ratio remained almost the same. The reason for the effect of AC on the carbon cluster was speculated. The mechanisms governing the conductivity behavior of the AC-modified SiCN werediscussed.
No preview · Article · Jul 2015 · Ceramics International
[Show abstract][Hide abstract] ABSTRACT: Mexiletine and lidocaine are widely used class IB anti-arrhythmic drugs that are considered to act by blocking voltage-gated open sodium currents for treatment of ventricular arrhythmias and relief of pain. To gain mechanistic insights into action of anti-arrhythmics, we characterized biophysical properties of Nav1.5 and Nav1.7 channels stably expressed in HEK293 cells and compared their use-dependent block in response to mexiletine and lidocaine using whole-cell patch clamp recordings. While the voltage-dependent activation of Nav1.5 or Nav1.7 was not affected by mexiletine and lidocaine, the steady-state fast and slow inactivation of Nav1.5 and Nav1.7 were significantly shifted to hyperpolarized direction by either mexiletine or lidocaine in dose-dependent manner. Both mexiletine and lidocaine enhanced the slow component of closed-state inactivation, with mexiletine exerting stronger inhibition on either Nav1.5 or Nav1.7. The recovery from inactivation of Nav1.5 or Nav1.7 was significantly prolonged by mexiletine compared to lidocaine. Furthermore, mexiletine displayed a pronounced and prominent use-dependent inhibition of Nav1.5 than lidocaine, but not Nav1.7 channels. Taken together, our findings demonstrate differential responses to blockade by mexiletine and lidocaine that preferentially affect the gating of Nav1.5, as compared to Nav1.7; and mexiletine exhibits stronger use-dependent block of Nav1.5. The differential gating properties of Nav1.5 and Nav1.7 in response to mexiletine and lidocaine may help explain the drug effectiveness and advance in new designs of safe and specific sodium channel blockers for treatment of cardiac arrhythmia or pain.
[Show abstract][Hide abstract] ABSTRACT: The AC conductive behavior of a polymer-derived amorphous silicon carbonitride ceramic was systemically studied. The conductivity exhibited a frequency-dependent switch: at low frequencies, the conductivity is constant and independent of frequency; while at high frequencies, the conductivity increases with frequency, showing a strong relaxation process. Both the frequency-independent conductivity and the characteristic frequency for the relaxation follow the Arrhenius relation with respect to the annealing temperature and follow a band-tail hopping process with respect to the testing temperature. XPS analysis revealed that a sp3–sp2 transition took place in the free-carbon phase of the material with increasing annealing temperature. The activation energy of the transition is similar to those for the Arrhenius relations. The following conductive mechanisms were proposed to account for the observed behaviors: the frequency-independent conductivity in the low frequency region is dominated by a long-distance transport of charge carriers via matrix-free carbon path, enhanced by an electric-field concentration effect; while the frequency-dependent conductivity in the high frequency region is dominated by a interfacial polarization process governed by charge carrier relaxation within the free-carbon phase.
[Show abstract][Hide abstract] ABSTRACT: The α7 nicotinic acetylcholine receptor (α7 nAChR) is an important and challenging target for drug discovery in the area of neuropsychiatric disorders. The current screening for chemicals targeting α7 nAChRs is primarily achieved by the use of low-throughput assay two-electrode voltage clamp (TEVC) in nonmammalian Xenopus oocytes. Automated patch clamp system has emerged as an attractive approach compared to conventional electrophysiology. To develop a mammalian cell-based functional assay in an automated electrophysiology system, we in this study generated a stable expression of α7 nAChRs in GH3 cells that originated from a rat pituitary tumor cell line and utilized automated QPatch-16 to test a set of tool compounds and chemicals identified as α7 agonists by TEVC. For the improvement of evaluating weak or partial α7 nAChRs agonists, we achieved enhancement of the signal-to-noise ratio by the addition of a positive allosteric modulator PNU-120596, which only activates α7 current in the presence of agonist. This improved assay was further validated by using known α7 partial agonists, such as RG3487, EVP-6124, and A-P90. Using this validated assay, we were able to identify a novel agonist 140507C that partially activates α7 nAChRs. Taken together, our results validate the use of QPatch-16 for evaluation α7 partial agonists, demonstrating its utility as an effective tool for α7 ion channel drug discovery.
No preview · Article · Apr 2015 · Assay and Drug Development Technologies
[Show abstract][Hide abstract] ABSTRACT: Protective coatings are critical to the successful application of the carbon/carbon (C/C) composites in the thermal protection systems of space vehicles. The damages of such coatings during installation and operation would threaten the safety of flight. In this contribution, an in-field technology based on a multilayer structure was developed to repair the damaged coatings of C/C composites. The multilayer structure contains a silicon buffer inner layer, a mullite heat-resistant middle layer and a borosilicate glass outer layer. The oxidation tests in air at 1300 °C and 1500 °C indicated that the weight loss of the repaired samples was greatly reduced compared with that of the damaged ones. The plasma wind tunnel tests for both repaired and damaged coatings further demonstrated that the multilayer structure could effectively protect the damaged composites from ablation in oxidation environments.
No preview · Article · Feb 2015 · Ceramics International
[Show abstract][Hide abstract] ABSTRACT: The detailed structural evolutions in polycarbosilane-derived carbon-rich amorphous SiC were investigated semi-quantitatively by combining experimental and analytical methods. It is revealed that the material comprised of a Si-containing matrix phase and a free carbon phase. The matrix phase is amorphous comprising of SiC4 tetrahedra, SiCxOx-4 tetrahedra and Si-C-C-Si/Si-C-H defects. With increasing pyrolysis temperature, the amorphous matrix becomes more order accompanied by a transition from SiC2O2 to SiCO3. The transition was completed at 1250oC, where the matrix phase started to crystallize by forming a small amount of -SiC. The free-carbon phase comprised of carbon nano-clusters and C-dangling bonds. Increasing pyrolysis temperature led to the transition of the free carbon from amorphous carbon to nanocrystalline graphite. The size of the carbon clusters decreased first and then increased, while the C-dangling bond content decreased continuously. The growth of carbon clusters was attributed to the Ostward ripening and described using 2-dimension grain growth model. The calculated activation energy suggested that the decrease in C-dangling bonds is directly related to the lateral growth of the carbon clusters.
No preview · Article · Dec 2014 · The Journal of Physical Chemistry A
[Show abstract][Hide abstract] ABSTRACT: A-type Kv4 potassium channels undergo a conformational change toward a nonconductive state at negative membrane potentials, a dynamic process known as pre-open closed states or closed-state inactivation (CSI). CSI causes inhibition of channel activity without the prerequisite of channel opening, thus providing a dynamic regulation of neuronal excitability, dendritic signal integration, and synaptic plasticity at resting. However, the structural determinants underlying Kv4 CSI remain largely unknown. We recently showed that the auxiliary KChIP4a subunit contains an N-terminal Kv4 inhibitory domain (KID) that directly interacts with Kv4.3 channels to enhance CSI. In this study, we utilized the KChIP4a KID to probe key structural elements underlying Kv4 CSI. Using fluorescence resonance energy transfer two-hybrid mapping and bimolecular fluorescence complementation-based screening combined with electrophysiology, we identified the intracellular tetramerization (T1) domain that functions to suppress CSI and serves as a receptor for the binding of KID. Disrupting the Kv4.3 T1-T1 interaction interface by mutating C110A within the C3H1 motif of T1 domain facilitated CSI and ablated the KID-mediated enhancement of CSI. Furthermore, replacing the Kv4.3 T1 domain with the T1 domain from Kv1.4 (without the C3H1 motif) or Kv2.1 (with the C3H1 motif) resulted in channels functioning with enhanced or suppressed CSI, respectively. Taken together, our findings reveal a novel (to our knowledge) role of the T1 domain in suppressing Kv4 CSI, and that KChIP4a KID directly interacts with the T1 domain to facilitate Kv4.3 CSI, thus leading to inhibition of channel function.
[Show abstract][Hide abstract] ABSTRACT: The electronic structure of polymer-derived amorphous silicon carbide ceramics was studied by combining measurements of temperature-dependent conductivity and optical absorption. By comparing the experimental results to theoretical models, electronic structure was constructed for a carbon-rich amorphous silicon carbide, which revealed several unique features, such as deep defect energy level, wide band-tail band, and overlap between the band-tail band and defect level. These unique features were discussed in terms of the microstructure of the material and used to explain the electric behavior.
No preview · Article · Jun 2014 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: We studied the electric conductivity and structure of polymer-derived carbon-rich amorphous SiC pyrolyzed at different temperatures. The conductivity of the material increased drastically with pyrolysis temperature followed an Arrhenius relationship with the activation energy of ~3.4 eV. Raman and X-ray photoelectron spectroscopy analysis revealed that the order of free carbon phase increased with pyrolysis temperature, accompanied by sp3→sp2 transition. The activation energy for such a structure change was 3.1–3.8 eV, which is close to that for the conductivity change. We thus believe that the increase in the conductivity was mainly due to the increase in conductivity of the free carbon phase.
No preview · Article · Apr 2014 · Journal of the American Ceramic Society
[Show abstract][Hide abstract] ABSTRACT: In this paper, we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors. A silazane oligmer and styrene monomer were used as starting materials, which were copolymerized at 120 oC to form random polypolysilazane-polystyrene copolymers. The copolymers were then pyrolyzed at 500 °C to obtain porous ceramics by completely decomposing polystyrene (PS) and converting polysilazane (PSZ) into non-oxide Si–C–N ceramics. The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than 500 m2/g. We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks. Current results suggest a promising simple method for making multi-scaled porous non-oxide materials.
No preview · Article · Apr 2014 · Journal of Materials Science and Technology -Shenyang-
[Show abstract][Hide abstract] ABSTRACT: The specific binding of auxiliary Kv channel-interacting proteins (KChIPs) to the N terminus of Kv4 pore-forming α-subunits results in modulation of gating properties, surface expression, and subunit assembly of Kv4 channels. However, the interactions between KChIPs and Kv4 remain elusive. Thus, affinity capillary electrophoresis (ACE) was employed to quantitatively evaluate the interactions between KChIPs and Kv4.3 N terminus (KvN) and between KChIP4a/related mutants and Ca2+ for the first time. The mobility ratio, derivatives calculated from the mobility shift method, was used to deduce the binding constants (Kb). As a result, the binding constants for KChIP4a/KvN and KChIP1/KvN complexes were (8.32 ± 1.66) × 106 L mol–1 and (5.26 ± 0.71) × 106 L mol–1, respectively. In addition, in the presence of calcium (10 μmol L–1), the binding constant of KChIP4a/KvN increased to (6.72 ± 1.66) × 107 L mol–1. In addition, the binding constant of KChIP4a with Ca2+ was (7.1 ± 1.5) × 107 L mol–1. Besides, studies on the effect of truncated mutants revealed that the third EF hand of KChIP4a was related to high-affinity binding with Ca2+, and the integrity of the molecular structure of KChIP4a was important for Ca2+ binding. This method profits from small samples, rapid analysis, and simple operation without being time-consuming.
No preview · Article · Mar 2014 · Analytical Biochemistry
[Show abstract][Hide abstract] ABSTRACT: Mtype potassium current (IM) was initially isolated from sympathetic neurons in 1980 and named as it was inhibited by muscarine. In 1998, the molecular identity of Mcurrent was revealed to be heterotetramers of KCNQ2 and KCNQ3 subunits, whose mutations cause neonatal epilepsy. Reduction of voltage-gated KCNQ2/3 K+ channel (M-channel) activity leads to neuronal hyperexcitability that defines the fundamental mechanism of neurological disorders such as epilepsy and pain. Thus, suppression of neuronal hyperexcitability by activation of KCNQ2/3 channels serves the basis for development of the channel openers for treatment of epilepsy and pain. The well-known KCNQ opener is retigabine (Potiga) that was approved by FDA as an antiepileptic drug in 2011. Recent studies also provide evidence that KCNQ2/3 channel openers are effective in animal models of bipolar disorder, anxiety and schizophrenia, whereas KCNQ2/3 inhibitors, on the other hand, are indicated for improvement of learning and memory in animal models. We recently designed and validated a novel series of pyrazolo [1,5a] pyrimidin7(4H)-ones (PPOs) that selectively activate KCNQ2/3 and show antiepileptic and analgesic activity in vivo. Up to date, all the progress made enforces the view that targeting voltage-gated KCNQ/M-channel may provide therapeutic potential for treatment of neuropsychiatric disorders
No preview · Article · Jan 2014 · Journal of Chinese Pharmaceutical Sciences