The Natural Flavonoid Naringenin Elicits Analgesia through Inhibition of NaV1.8 Voltage-Gated Sodium Channels.

Naringenin (2S)-5,7-dihydroxy-2-(4-hydroxyphenyl)-3,4-dihydro-2H-1-benzopyran-4-one is a natural flavonoid found in fruits from the citrus family. Because (2S)-naringenin is known to racemize, its bioactivity might be related to one or both enantiomers. Computational studies predicted that (2R)-naringenin may act on voltage-gated ion channels, particularly the N-type calcium channel (CaV2.2) and the NaV1.7 sodium channel-both of which are key for pain signaling. Here we set out to identify the possible mechanism of action of naringenin. Naringenin inhibited depolarization-evoked Ca2+ influx in acetylcholine-, ATP-, and capsaicin-responding rat dorsal root ganglion (DRG) neurons. This was corroborated in electrophysiological recordings from DRG neurons. Pharmacological dissection of each of the voltage-gated Ca2+ channels subtypes could not pinpoint any selectivity of naringenin. Instead, naringenin inhibited NaV1.8-dependent and tetrodotoxin (TTX)-resistant while sparing tetrodotoxin sensitive (TTX-S) voltage-gated Na+ channels as evidenced by the lack of further inhibition by the NaV1.8 blocker A-803467. The effects of the natural flavonoid were validated ex vivo in spinal cord slices where naringenin decreased both the frequency and amplitude of sEPSC recorded in neurons within the substantia gelatinosa. The antinociceptive potential of naringenin was evaluated in male and female mice. Naringenin had no effect on the nociceptive thresholds evoked by heat. Naringenin's reversed allodynia was in mouse models of postsurgical and neuropathic pain. Here, driven by a call by the National Center for Complementary and Integrative Health's strategic plan to advance fundamental research into basic biological mechanisms of the action of natural products, we advance the antinociceptive potential of the flavonoid naringenin.

Evaluation of the anticancer and anti-metastasis effects of novel synthetic sodium channel blockers in prostate cancer cells in vitro and in vivo.

BACKGROUND: Voltage-gated sodium channels (VGSCs) are involved in several cellular processes related to cancer cell growth and metastasis, including adhesion, proliferation, apoptosis, migration, and invasion. We here in investigated the effects of S0154 and S0161, two novel synthetic sodium channel blockers (SCBs), on human prostate cancer cells (PC3, DU145, and LnCaP) and a prostate cancer xenograft model. METHODS: The MTT assay was used to assess the anticancer effects of SCBs in PC3, DU145, and LnCaP cells. Sodium indicator and glucose uptake assays were used to determine the effects of S0154 and S0161 in PC3 cells. The impact of these SCBs on the proliferation, cell cycle, apoptosis, migration, and invasion of PC3 cells were determined using a CFDA-SE cell proliferation assay, cell cycle assay, annexin V-FITC apoptosis assay, transwell cell invasion assay, and wound-healing assay, respectively. The protein expression levels of Nav1.6, Nav1.7, CDK1, cyclin B1, MMP2, MMP9 in PC3 cells were analysis by Western blotting. The in vivo anticancer activity was evaluated using a PC3 xenograft model in nude mice. RESULTS: S0154 and S0161 both showed anticancer and anti-metastatic effects against prostate cancer cells and significantly inhibited cell viability, with IC50 values in the range of 10.51-26.60 µmol/L (S0154) and 5.07-11.92 µmol/L (S0161). Both compounds also increased the intracellular level of sodium, inhibited the protein expression of two α subunits of VGSCs (Nav1.6 and Nav1.7), and caused G2/M phase cell cycle arrest, with no or minor effects on cell apoptosis. Concentrations of 5 and 10 µmol/L of S0154 and S0161 significantly decreased the glucose uptake of PC3 cells. The compounds also inhibited the proliferation of PC3 cells and decreased their invasion in transwell assays. Furthermore, S0161 exerted antitumor activity in an in vivo PC3 xenograft model in nude mice, inhibiting the growth of the tumors by about 51% compared to the control group. CONCLUSIONS: These results suggest that S0154 and S0161 have anticancer and anti-metastasis effects in prostate cancer cells both in vitro and in vivo, supporting their further development as potential therapeutic agents for prostate cancer.

Inhibitive effect of loureirin B plus capsaicin on tetrodotoxin-resistant sodium channel.

OBJECTIVE: To investigate whether the effect of loureirin B plus capsaicin on tetrodotoxin-resistant (TTX-R) sodium channel. METHODS: By using whole-cell patch-clamp recordings, in acutely isolated dorsal root ganglion (DRG) neurons, the combined effects of loureirin B and capsaicin on TTX-R sodium channel were observed. Based on the data, the interaction between loureirin B and capsaicin in their modulation on TTX-R sodium channel was assessed. RESULTS: Loureirin B could not induce transient inward TRPV1 current. Capsazepine, a transient receptor potential vanilloid l (TRPV1) antagonist, could not attenuate the block of 0.64 mmol/L loureirin B on TTX-R sodium channel. There was no significant difference (P > 0.05) between IC50 of loureirin B (0.37 mmol/L) on TTX-R sodium channel in capsaicin-sensitive DRG neurons and that (0.38 mmol/L) in capsaicin-insensitive DRG neurons. However, there was a significant difference (P < 0.05) between the IC50 of capsaicin (0.28 ¦Ìmol/L) on TTX-R sodium channel in capsaicin-sensitive DRG neurons and that (52.24 ¦Ìmol/L) in capsaicin-insensitive DRG neurons. Four combinations composed of various concentrations of loureirin B and capsaicin could all inhibit TTX-R sodium currents but have different interactions between loureirin B and capsaicin. CONCLUSION: Loureirin B plus capsaicin could produce double blockage on TRPV1 and modulation on TTX-R sodium channel. The action of loureirin B on TTX-R sodium channel was independent of TRPV1 but similar with that of capsaicin on TTX-R sodium channel in capsaicin-insensitive DRG neurons.

Choline but not its derivative betaine blocks slow vacuolar channels in the halophyte Chenopodium quinoa: implications for salinity stress responses.

Activity of tonoplast slow vacuolar (SV, or TPC1) channels has to be under a tight control, to avoid undesirable leak of cations stored in the vacuole. This is particularly important for salt-grown plants, to ensure efficient vacuolar Na(+) sequestration. In this study we show that choline, a cationic precursor of glycine betaine, efficiently blocks SV channels in leaf and root vacuoles of the two chenopods, Chenopodium quinoa (halophyte) and Beta vulgaris (glycophyte). At the same time, betaine and proline, two major cytosolic organic osmolytes, have no significant effect on SV channel activity. Physiological implications of these findings are discussed.

Isolation and identification of a sodium channel-inhibiting protein from eggs of black widow spiders.

The eggs of black widow spider (L. tredecimguttatus) have been demonstrated to be rich in biologically active components that exhibit great research value and application foreground. In the present study, a protein toxin, named Latroeggtoxin-II, was isolated from the eggs using the combination of gel filtration, ion exchange chromatography and reversed-phase high performance liquid chromatography. Electrospray mass spectrometric analysis indicated that the molecular weight of the protein was 28.69 kDa, and Edman degradation revealed that its N-terminal sequence was ESIQT STYVP NTPNQ KFDYE VGKDY-. After being abdominally injected into mice and P. americana, the protein could make the animals especially P. americana display a series of poisoning symptoms. Electrophysiological experiments demonstrated that the protein could selectively inhibit tetrodotoxin-resistant Na(+) channel currents in rat dorsal root ganglion neurons, without significant effect on the tetrodotoxin-sensitive Na(+) channel currents. Using multiple proteomic strategies, the purified protein was shown to have only a few similarities to the existing proteins in the databases, suggesting that it was a novel protein isolated from the eggs of black widow spiders.

Diterpene alkaloids from the roots of Aconitum moldavicum and assessment of Nav 1.2 sodium channel activity of aconitum alkaloids.

A new aconitane alkaloid, 1-O-demethylswatinine (1), was isolated from the root of Aconitum moldavicum together with the known compounds cammaconine (2), columbianine (3), swatinine (4), gigactonine (5), delcosine (6), lycoctonine (7), and ajacine (8). The structures were established by means of HRESIMS, 1D and 2D NMR spectroscopy, including 1H-1H COSY, NOESY, HSQC, and HMBC experiments, resulting in complete 1H-NMR chemical shift assignments for 1-4. The effects of the isolated compounds 4-8, together with eighteen other Aconitum diterpene and norditerpene alkaloids with different skeletal types and substitution patterns, were studied on Nav 1.2 channels by the whole-cell patch clamp technique, using the QPatch-16 automated patch clamp system. Pyroaconitine, ajacine, septentriodine, and delectinine demonstrated significant Nav 1.2 channel inhibition (57-42 %) at 10 µM concentration; several other compounds (acovulparine, acotoxicine, hetisinone, 14-benzoylaconine-8-O-palmitate, aconitine, and lycoctonine) exerted moderate inhibitory activity (30-22 %), while the rest of the tested alkaloids were considered to be inactive. On the basis of these results and by exhaustive comparison of data of previously published computerized QSAR studies on diterpene alkaloids, certain conclusions on the structure-activity relationships of Aconitum alkaloids concerning Nav 1.2 channel inhibitory activity are proposed.

Semicarbazone analogs as anticonvulsant agents: a review.

Semicarbazones are synthesized by the condensation of semicarbazide and aldehyde/ketone. The literature survey revealed that semicarbazones had been emerged as compounds with diverse biological activities including anticonvulsant, antitubercular, anticancer, and antimicrobial activities. The anticonvulsant activity of semicarbazones is mainly attributed due to the presence of an aryl binding site with aryl/alkyl hydrophobic group, a hydrogen bonding domain and an electron donor group and they are suggested to act by inhibiting sodium ion (Na(+)) channel. Dimmock et al., reported an extensive series of semicarbazones and reported 4-(4-fluorophenoxy) benzaldehyde semicarbazone (C0102862, V102862) as lead molecule. In MES (oral) screening C0102862 showed protective index (PI > 315) more than carbamazepine (PI 101), phenytoin (PI > 21.6) and valproate (PI > 2.17). This review briefly describes the information available about semicarbazone analogs and their anticonvulsant activity.

Inhibition of human Na(v)1.5 sodium channels by strychnine and its analogs.

Strychnine and brucine from the seeds of the plant Strychnos nux vomica have been shown to have interesting pharmacological effects on several neurotransmitter receptors. In this study, we have characterized the pharmacological properties of strychnine and its analogs on human Na(v)1.5 channels to assess their potential therapeutic advantage in certain arrhythmias. Among the eight alkaloids, only strychnine and icajine exhibited inhibition potency on the Na(v)1.5 channel with the half-maximum inhibition (IC(50)) values of 83.1µM and 104.6µM, respectively. Structure-function analysis indicated that the increased bulky methoxy groups on the phenyl ring or the negatively charged oxygen atom may account for this lack of inhibition on the Na(v)1.5 channel. Strychnine and icajine may bind to the channel by cation-π interactions. The substitution with a large side chain on the phenyl ring or the increased molecular volume may alter the optimized position for the compound close to the binding sites of the channel. Strychnine and icajine bind to the Na(v)1.5 channel with a new mechanism that is different from TTX and local anesthetics. They bind to the outer vestibule of the channel pore with fast association and dissociation rates at resting state. Strychnine and icajine had little effect on steady-state fast inactivation but markedly shifted the slow inactivation of Na(v)1.5 currents toward more hyperpolarized potentials. The property of icajine influencing slow-inactivated state of Na(v)1.5 channel would be potential therapeutic advantages in certain arrhythmias.

Discovery of a novel class of biphenyl pyrazole sodium channel blockers for treatment of neuropathic pain.

A series of novel biphenyl pyrazole dicarboxamides were identified as potential sodium channel blockers for treatment of neuropathic pain. Compound 20 had outstanding efficacy in the Chung rat spinal nerve ligation (SNL) model of neuropathic pain.

Discovery and biological evaluation of potent, selective, orally bioavailable, pyrazine-based blockers of the Na(v)1.8 sodium channel with efficacy in a model of neuropathic pain.

Na(v)1.8 (also known as PN3) is a tetrodotoxin-resistant (TTx-r) voltage-gated sodium channel (VGSC) that is highly expressed on small diameter sensory neurons. It has been implicated in the pathophysiology of inflammatory and neuropathic pain, and we envisioned that selective blockade of Na(v)1.8 would be analgesic, while reducing adverse events typically associated with non-selective VGSC blocking therapeutic agents. Herein, we describe the preparation and characterization of a series of 6-aryl-2-pyrazinecarboxamides, which are potent blockers of the human Na(v)1.8 channel and also block TTx-r sodium currents in rat dorsal root ganglia (DRG) neurons. Selected derivatives display selectivity versus human Na(v)1.2. We further demonstrate that an example from this series is orally bioavailable and produces antinociceptive activity in vivo in a rodent model of neuropathic pain following oral administration.

A-887826 is a structurally novel, potent and voltage-dependent Na(v)1.8 sodium channel blocker that attenuates neuropathic tactile allodynia in rats.

Activation of sodium channels is essential to action potential generation and propagation. Recent genetic and pharmacological evidence indicates that activation of Na(v)1.8 channels contributes to chronic pain. Herein, we describe the identification of a novel series of structurally related pyridine derivatives as potent Na(v)1.8 channel blockers. A-887826 exemplifies this series and potently (IC(50)=11nM) blocked recombinant human Na(v)1.8 channels. A-887826 was approximately 3 fold less potent to block Na(v)1.2, approximately 10 fold less potent to block tetrodotoxin-sensitive sodium (TTX-S Na(+)) currents and was >30 fold less potent to block Na(V)1.5 channels. A-887826 potently blocked tetrodotoxin-resistant sodium (TTX-R Na(+)) currents (IC(50)=8nM) from small diameter rat dorsal root ganglion (DRG) neurons in a voltage-dependent fashion. A-887826 effectively suppressed evoked action potential firing when DRG neurons were held at depolarized potentials and reversibly suppressed spontaneous firing in small diameter DRG neurons from complete Freund's adjuvant inflamed rats. Following oral administration, A-887826 significantly attenuated tactile allodynia in a rat neuropathic pain model. Further characterization of TTX-R current block in rat DRG neurons demonstrated that A-887826 (100nM) shifted the mid-point of voltage-dependent inactivation of TTX-R currents by approximately 4mV without affecting voltage-dependent activation and did not exhibit frequency-dependent inhibition. The present data demonstrate that A-887826 is a structurally novel and potent Na(v)1.8 blocker that inhibits rat DRG TTX-R currents in a voltage-, but not frequency-dependent fashion. The ability of this structurally novel Na(v)1.8 blocker to effectively reduce tactile allodynia in neuropathic rats further supports the role of Na(v)1.8 sodium channels in pathological pain states.

Design and assessment of a potent sodium channel blocking derivative of mexiletine for minimizing experimental neuropathic pain in several rat models.

Physical or chemical damage to peripheral nerves can result in neuropathic pain which is not easily alleviated by conventional analgesic drugs. Substantial evidence has demonstrated that voltage-gated Na+ channels in the membrane of damaged nerves play a key role in the establishment and maintenance of pathological neuronal excitability not only of these peripheral nerves but also in the second- and third-order neurons in the pain pathway to the cerebral cortex. Na+ channel blocking drugs have been used in treating neuropathic pain with limited success mainly because of a preponderance of side-effects. We have developed an analogue of mexiletine which is approximately 80 times more potent than mexiletine in competing with the radioligand, 3H-batrachotoxinin for binding to Na+ channels in rat brain membranes and also it is much more lipophilic than mexiletine which should enhance its uptake into the brain to block the increased expression of Na+ channels on second- and third-order neurons of the pain pathway. This analogue, HFI-1, has been tested in three different rat models of neuropathic pain (formalin paw model, ligated spinal nerve model and contusive spinal cord injury model) and found to be more effective in reducing pain behaviours than mexiletine.

Prediction of ion channel activity using binary kernel discrimination.

Voltage-gated ion channels are a diverse family of pharmaceutically important membrane proteins for which limited 3D information is available. A number of virtual screening tools have been used to assist with the discovery of new leads and with the analysis of screening results. One such tool, and the subject of this paper, is binary kernel discrimination (BKD), a machine-learning approach that has recently been applied to applications in chemoinformatics. It uses a training set of compounds, for which both structural and qualitative activity data are known, to produce a model that can then be used to rank another set of compounds in order of likely activity. Here, we report the use of BKD to build models for the prediction of five different ion channel targets using two types of activity data. The results obtained suggest that the approach provides an effective way of prioritizing compounds for acquisition and testing.

Liquisolid technique for dissolution rate enhancement of a high dose water-insoluble drug (carbamazepine).

Different liquisolid formulations of carbamazepine were accomplished by dissolving the drug in the non-toxic hydrophilic liquids, and adsorbing the solution onto the surface of silica. In order to reduce the amounts of carrier and aerosil in liquisolid formulations, some additives namely polyvinylpyrrolidone (PVP), hydroxypropyle methylcellulose (HPMC) and polyethylene glycol (PEG 35000) were added to liquid medication to increase loading factor. The effects of various ratios of carrier to coating material, PVP concentration, effect of aging and type of the carrier on dissolution rate of liquisolid compacts were studied. X-ray crystallography and differential scanning calorimetery (DSC) were used for evaluation of physicochemical properties of carbamazepine in liquisolid formulations. The results showed that the drug loading factor was increased significantly in the presence of additives. Liquisolid formulations containing PVP as additive, exhibited significantly higher drug dissolution rates compared to the compacts prepared by the direct compression technique. It was shown that microcrystalline cellulose had more liquid retention potential in comparison with lactose, and the formulations containing microcrystalline cellulose as carrier, showed higher dissolution rate. By decreasing the ratio of microcrystalline cellulose to silica from 20 to 10, an improvement in dissolution rate was observed. Further decrease in the ratio of microcrystalline cellulose:silica from 10 to 5 resulted in a significant reduction in dissolution rate. Increasing of PVP concentration in liquid medication caused a dramatic increase in dissolution rate at first 30min. The results showed that the dissolution rate of liquisolid tablets was not significantly affected by storing the tablets at 25 degrees C/75% relative humidity for a period of 6 months. The results of DSC and X-ray crystallography did not show any changes in crystallinity of the drug and interaction between carbamazepine and exipients during the process.

Solution structure and functional characterization of jingzhaotoxin-XI: a novel gating modifier of both potassium and sodium channels.

JZTX-XI is a peptide toxin isolated from the venom of the Chinese spider Chilobrachys jingzhao. It contains 34 residues including six cysteine residues with disulfide bridges linked in the pattern of I-IV, II-V, and III-VI. Using 3'- and 5'-RACE methods, the full-length cDNA was identified as encoding an 86-residue precursor of JZTX-XI. In the electrophysiological assay, JZTX-XI shows activity toward the Kv2.1 channel in a way similar to hanatoxin1 and SGTx1 that both the activation and the deactivation processes are affected, which is in accordance with the high sequence homology among them (over 60% identity). On the other hand, JZTX-XI also exhibits specific interaction against the Nav channels of rat cardiac myocytes with a significant reduction in the peak current and slowing of channel inactivation. The solution structure of native JZTX-XI was determined by 1H NMR methods to identify the structural basis of these specific activities. Structural comparison of JZTX-XI with other gating modifier toxins shows that they all adopt a similar surface profile, a hydrophobic patch surrounded by charged residues such as Arg or Lys, which might be a common structural factor responsible for toxin-channel interaction. JZTX-XI might be an ideal tool to further investigate how spider toxins recognize various ion channels as their targets.

Synthesis and biological evaluation of new 4-arylpiperidines and 4-aryl-4-piperidinols: dual Na(+) and Ca(2+) channel blockers with reduced affinity for dopamine D(2) receptors.

A series of novel 4-arylpiperidines and 4-aryl-4-piperidinols (2a-f, 3a-f and 4a-f) was synthesized and evaluated for blocking effects on both neuronal Na(+) and T-type Ca(2+) channels and binding affinity for dopamine D(2) receptors. Most of the compounds blockaded both ion channels with potency greater than or equal to flunarizine 1a which was adopted as a reference standard. In addition, these compounds had significantly reduced affinity for dopamine D(2) receptors which is common in this class of structure. Compounds 2a-f, 3a-f and 4a-f exhibited potent anticonvulsant effects following systemic (ip) administration on audiogenic seizures in DBA/2 mice, indicating their excellent brain permeability. The neuroprotective activity of 2a, 3a and 4a was also assessed in a transient middle cerebral artery occlusion (MCAO) model. These compounds significantly reduced neuronal damage without affecting ischemic hyperthemia, while flunarizine 1a produced only minor reductions. In particular, 4a had 1.7-fold the potency in this MCAO model but only 1/20 the affinity for dopamine D(2) receptors of 1a. The superposition of 2a, 3a and 4a on the basis of analyses of systematic conformation and similar structure has revealed that the cinnamyl, phenacyl and phenoxypropanol groups are likely to be structurally and biologically equivalent. Moreover, the superposition of 2a and 2f shows that diphenyl ether and biphenyl groups occupy a similar space, suggesting that both groups act as a bioisostere for the blockade of ion channels; however, this is not the case for dopamine D(2) receptors since only biphenyl compounds such as 2f had high affinity similar to flunarizine 1a. Compound 4a (SUN N5030) has a good pharmacological profile and may be useful in the alleviation and treatment of ischemic diseases.