Tae-Joon Shin

Gintonin, Newly Identified Compounds from Ginseng, Is Novel Lysophosphatidic Acids-Protein Complexes and Activates G Protein-Coupled Lysophosphatidic Acid Receptors with High Affinity

Recently, we isolated a subset of glycolipoproteins from Panax ginseng, that we designated gintonin, and demonstrated that it induced [Ca2+]i transients in cells via G-protein-coupled receptor (GPCR) signaling pathway(s). However, active components responsible for Ca2+ mobilization and the corresponding receptor(s) were unknown. Active component(s) for [Ca2+]i transients of gintonin were analyzed by liquid chromatography-electrospray ionization-tandem mass spectrometry and ion-mobility mass spectrometry, respectively. The corresponding receptor(s) were investigated through gene expression assays. We found that gintonin contains LPA C18:2 and other LPAs. Proteomic analysis showed that ginseng major latex-like protein and ribonuclease-like storage proteins are protein components of gintonin. Gintonin induced [Ca2+]i transients in B103 rat neuroblastoma cells transfected with human LPA receptors with high affinity in order of LPA2 > LPA5 > LPA1 > LPA3 > LPA4. The LPA1/LPA3 receptor antagonist Ki16425 blocked gintonin action in cells expressing LPA1 or LPA3. Mutations of binding sites in the LPA3 receptor attenuated gintonin action. Gintonin acted via pertussis toxin (PTX)-sensitive and -insensitive G protein-phospholipase C (PLC)-inositol 1,4,5-trisphosphate (IP3)-Ca2+ pathways. However, gintonin had no effects on other receptors examined. In human umbilical vein endothelial cells (HUVECs) gintonin stimulated cell proliferation and migration. Gintonin stimulated ERK1/2 phosphorylation. PTX blocked gintonin-mediated migration and ERK1/2 phosphorylation. In PC12 cells gintonin induced morphological changes, which were blocked by Rho kinase inhibitor Y-27632. Gintonin contains GPCR ligand LPAs in complexes with ginseng proteins and could be useful in the development of drugs targeting LPA receptors.

Gintonin, a Ginseng-Derived Lysophosphatidic Acid Receptor Ligand, Attenuates Alzheimer's Disease-Related Neuropathies: Involvement of Non-Amyloidogenic Processing

Ginseng extracts show cognition-enhancing effects in Alzheimers disease (AD) patients. However, little is known about the active components and molecular mechanisms of how ginseng exerts its effects. Recently, we isolated a novel lysophosphatidic acid (LPA) receptor-activating ligand from ginseng, gintonin. AD is caused by amyloid-β protein (Aβ) accumulation. Aβ is derived from amyloid-β protein precursors (AβPPs) through the amyloidogenic pathway. In contrast, non-amyloidogenic pathways produce beneficial, soluble AβPPα (sAβPPα). Here, we describe our investigations of the effect of gintonin on sAβPPα release, Aβ formation, Swedish-AβPP transfection-mediated neurotoxicity in SH-SY5Y neuroblastoma cells, and Aβ-induced neuropathy in mice. Gintonin promoted sAβPPα release in a concentration- and time-dependent manner. Gintonin action was also blocked by the Ca2+ chelator BAPTA, α-secretase inhibitor TAPI-2, and protein-trafficking inhibitor brefeldin. Gintonin decreased Aβ1-42 release and attenuated Aβ1-40-induced cytotoxicity in SH-SY5Y cells. Gintonin also rescued Aβ1-40-induced cognitive dysfunction in mice. Moreover, in a transgenic mouse AD model, long-term oral administration of gintonin attenuated amyloid plaque deposition as well as short- and long-term memory impairment. In the present study, we demonstrated that gintonin mediated the promotion of non-amyloidogenic processing to stimulate sAβPPα release to restore brain function in mice with AD. Gintonin could be a useful agent for AD prevention or therapy.

A simple method for the preparation of crude gintonin from ginseng root, stem, and leaf.

Ginseng has been used as a general tonic agent to invigorate the human body as an adaptogenic agent. In a previous report, we have shown that ginseng contains a novel glycolipoprotein called gintonin. The main function of gintonin is to transiently enhance intracellular free Ca2+ [Ca2+]i levels in animal cells. The previous method for gintonin isolation included multiple steps using organic solvents. In the present report, we developed a simple method for the preparation of crude gintonin from ginseng root as well as stem and leaf, which produced a higher yield of gintonin than the previous one. The yield of gintonin was 0.20%, 0.29%, and 0.81% from ginseng root, stem, and leaf, respectively. The apparent molecular weight of gintonin isolated from stem and leaf through sodium dodecyl sulfate polyacrylamide gel electrophoresis was almost same as that from root but the compositions of amino acids, carbohydrates or lipids differed slightly between them. We also examined the effects of crude gintonin from ginseng root, stem, and leaf on endogenous Ca2+-activated Cl- channel (CaCC) activity of Xenopus oocytes through mobilization of [Ca2+]i. We found that the order of potency for the activation of CaCC was ginseng root > stem > leaf. The ED50 was 1.4±1.4, 4.5±5.9, and 3.9±1.1 μg/mL for root, stem and leaf, respectively. In the present study, we demonstrated for the first time that in addition to ginseng root, ginseng stem and leaf also contain gintonin. Gintonin can be prepared from a simple method with higher yield of gintonin from ginseng root, stem, and leaf. Finally, these results demonstrate the possibility that ginseng stem and leaf could also be utilized for ginstonin preparation after a simple procedure, rather than being discarded.

Effects of Minor Ginsenosides, Ginsenoside Metabolites, and Ginsenoside Epimers on the Growth of Caenorhabditis elegans

In the previous report, we have demonstrated that ginsenoside Rc, one of major ginsenosides, is a major component for the restoration for normal growth of worms in cholesterol-deprived medium. In the present study, we further investigated the roles of minor ginsenosides, such as ginsenoside Rh1 and Rh2, ginsenoside metabolites such as compound K (CK), protopanaxadiol (PPD), and protopanaxatriol (PPT) and ginsenoside epimers such as 20(R)- and 20(S)-ginsenoside Rg3 in cholesterol-deprived medium. We found that ginsenoside Rh1 almost restored normal growth of worms in cholesterol-deprived medium in F1 generation. However, supplement of ginsenoside Rh2 caused a suppression of worm growths in cholesterol-deprived medium. In addition, CK and PPD also slightly restored normal growth of worms in cholesterol-deprived medium but PPT not. In experiments using ginsenoside epimers, supplement of 20(S)- but not 20(R)-ginsenoside Rg3 in cholesterol-deprived medium also almost restored worm growth. These results indicate that the absence or presence of carbohydrate component at backbone of ginsenoside, the number of carbohydrate attached at carbon-3, and the position of hydroxyl group at carbon-20 of ginsenoside might plays important roles in restoration of worm growth in cholesterol-deprived medium.

Ginsenoside Rg3 activates human KCNQ1 K+ channel currents through interacting with the K318 and V319 residues: a role of KCNE1 subunit.

The slowly activating delayed rectifier K(+) channels (I(Ks)) are one of the main pharmacological targets for development of drugs against cardiovascular diseases. Cardiac I(Ks) consists of KCNQ1 plus KCNE1 subunits. Ginsenoside, one of the active ingredient of Panax ginseng, enhances cardiac I(Ks) currents. However, little is known about the molecular mechanisms of how ginsenoside interacts with channel proteins to enhance cardiac I(Ks). In the present study, we investigated ginsenoside Rg(3) (Rg(3)) effects on human I(Ks) by co-expressing human KCNQ1 plus KCNE1 subunits in Xenopus oocytes. Rg(3) enhanced I(Ks) currents in concentration- and voltage-dependent manners. The EC(50) was 15.2+/-8.7 microM. However, in oocytes expressing KCNQ1 alone, Rg(3) inhibited the currents with concentration- and voltage-dependent manners. The IC(50) was 4.8+/-0.6 microM. Since Rg(3) acts opposite ways in oocytes expressing KCNQ1 alone or KCNQ1 plus KCNE1 subunits, we examined Rg(3) effects after co-expression of different ratios of KCNE1 and KCNQ1. The increase of KCNE1/KCNQ1 ratio converted I(Ks) inhibition to I(Ks) activations. One to ten ratio of KCNE1 and KCNQ1 subunit is required for Rg(3) activation of I(Ks). Mutations of K318 and V319 into K318Y and V319Y of KCNQ1 channel abolished Rg(3) effects on KCNQ1 or KCNQ1 plus KCNE1 channel currents. The docked modeling revealed that K318 residue plays a key role in stabilization between Rg(3) and KCNQ1 plus KCNE1 or KCNQ1 subunit. These results indicate that Rg(3)-induced activation of I(Ks) requires co-assembly of KCNQ1 and KCNE1 subunits and achieves this through interaction with residues K318 and V319 of KCNQ1 subunit.

Ginsenoside Rg3 decelerates hERG K+ channel deactivation through Ser631 residue interaction

The human ether-a-go-go-related gene (hERG) cardiac K(+) channels are one of the representative pharmacological targets for development of drugs against cardiovascular diseases such as arrhythmia. Panax ginseng has been known to have cardio-protective effects. However, little is known about the molecular mechanisms of how ginsenosides, the active ingredients in Panax ginseng, interact with hERG K(+) channel proteins. In the present study, we first examined the effects of various ginsenosides on hERG K(+) channel activity by expressing human α subunits in Xenopus oocytes. Among them ginsenoside Rg(3) (Rg(3)) most potently enhanced outward I(hERG) and peak I(tail). Rg(3) induced a large persistent deactivating-tail current (I(deactivating-tail)) and profoundly decelerated deactivating current decay in both concentration- and voltage-dependent manners. The EC(50) for steady-state I(hERG), peak I(tail), and persistent I(deactivating-tail) was 0.41±0.05, 0.61±0.11, and 0.36±0.04μM, respectively. Rg(3) actions were blocked by bepridil, a hERG K(+) channel antagonist. Site-directed mutation of S631, which is located at the channel pore entryway, to S631C in hERG K(+) channel abolished Rg(3) actions on hERG K(+) channels. These results indicate that S631 residue of hERG K(+) channel plays an important role in Rg(3)-mediated induction of a persistent I(deactivating-tail) and in a deceleration of hERG K(+) channel deactivation.

Effects of quercetin on α9α10 nicotinic acetylcholine receptor-mediated ion currents

Quercetin, one of the flavonoids, is a low molecular weight substance found in fruits and vegetables. Quercetin, like other flavonoids, has a wide range of neuropharmacological actions and antioxidant effects. The α9α10 nicotinic acetylcholine receptor is one of the numerous nicotinic acetylcholine receptors that exist as a heteropentameric form between efferent olivocochlear fibers and hair cells of the cochlea. In this study, we report the effects of quercetin on rat α9α10 nicotinic acetylcholine receptor-mediated ion currents using the two-electrode voltage-clamp technique. Treatment with acetylcholine evoked inward currents (I(ACh)) in oocytes heterologously expressing the α9α10 nicotinic acetylcholine receptor. Quercetin blocked I(ACh) in concentration-dependent and reversible manners, and the blocking effect on I(ACh) was stronger with pre-application than co-application of quercetin. The half maximal inhibitory concentration (IC(50)) of quercetin was 45.4±10.1μM. Quercetin-mediated I(ACh) inhibition was not affected by acetylcholine concentration and was independent of membrane-holding potential. Although the inhibitory effect of quercetin was significantly attenuated in the absence of extracellular Ca(2+), the action of quercetin was independent of extracellular Ca(2+) concentration, indicating that the presence of extracellular Ca(2+) might be needed for quercetin-related effects and might play an important role in quercetin-mediated regulation of the α9α10 nicotinic acetylcholine receptor. These results indicate that quercetin-mediated regulation of the α9α10 nicotinic acetylcholine receptor could provide a molecular basis for quercetin actions at the cellular level.

Ginsenoside Rg3 enhances large conductance Ca2+-activated potassium channel currents: A role of Tyr360 residue

Ginsenosides, active ingredients of Panax ginseng, are known to exhibit neuroprotective effects. Large-conductance Ca2+-activated K+ (BKCa) channels are key modulators of cellular excitability of neurons and vascular smooth muscle cells. In the present study, we examined the effects of ginsenosides on rat brain BKCa (rSlo) channel activity heterologously expressed in Xenopus oocytes to elucidate the molecular mechanisms how ginsenoside regulates the BKCa channel activity. Ginsenoside Rg3 (Rg3) enhanced outward BKCa channel currents. The Rg3-enhancement of outward BKCa channel currents was concentration-dependent, voltage-dependent, and reversible. The EC50 was 15.1 ± 3.1 μM. Rg3 actions were not desensitized by repeated treatment. Tetraetylammonium (TEA), a K+ channel blocker, inhibited BKCa channel currents. We examined whether extracellular TEA treatment could alter the Rg3 action and vice versa. TEA caused a rightward shift of the Rg3 concentration-response curve (i.e., much higher concentration of Rg3 is required for the activation of BKCa channel compared to the absence of TEA), while Rg3 caused a rightward shift of the TEA concentration-response curve in wild-type channels. Mutation of the extracellular TEA binding site Y360 to Y360I caused a rightward shift of the TEA concentration-response curve and almost abolished both the Rg3 action and Rg3-induced rightward shift of TEA concentration-response curve. These results indicate that Tyr360 residue of BKCa channel plays an important role in the Rg3-enhancement of BKCa channel currents.

Quercetin enhances human α7 nicotinic acetylcholine receptor-mediated ion current through interactions with Ca2+ binding sites

The flavonoid quercetin is a low molecular weight substance found in fruits and vegetables. Aside from its anti-oxidative effect, quercetin, like other flavonoids, has a wide range of neuropharmacological actions. The α7 nicotinic acetylcholine receptor (α7 nAChR) has a Ca2+-binding site, is highly permeable to the Ca2+ ion, and plays important roles in Ca2+-related normal brain functions. Dysfunctions of α7 nAChR are associated with a variety of neurological disorders. In the present study, we investigated the effects of quercetin on the ACh-induced inward peak current (IACh) in Xenopus oocytes that heterologously express human α7 nAChR. IACh was measured with the two-electrode voltage clamp technique. In oocytes injected with α7 nAChR cRNA, the effects of the co-application of quercetin on IACh were concentration-dependent and reversible. The ED50 was 36.1 + 6.1 μM. Quercetin-mediated enhancement of IACh caused more potentiation when quercetin was pre-applied. The degree of IACh potentiation by quercetin pre-application was time-dependent and saturated after 1 min. Quercetin-mediated IACh enhancement was not affected by ACh concentration and was voltage-independent. However, quercetin-mediated IACh enhancement was dependent on extracellular Ca2+ concentrations and was specific to the Ca2+ ion, since the removal of extracellular Ca2+ or the addition of Ba2+ instead of Ca2+ greatly diminished quercetin enhancement of IACh. The mutation of Glu195 to Gln195, in the Ca2+-binding site, almost completely diminished quercetin-mediated IACh enhancement. These results indicate that quercetin-mediated IACh enhancement human α7 nAChR heterologously expressed in Xenopus oocytes could be achieved through interactions with the Ca2+-binding site of the receptor.

Differential Effects of Ginsenoside Metabolites on HERG K + Channel Currents

The human ether-a-go-go-related gene (HERG) cardiac K+ channels are one of the representative pharmacological targets for development of drugs against cardiovascular diseases such as arrhythmia. Panax ginseng has been known to exhibit cardioprotective effects. In a previous report we demonstrated that ginsenoside Rg3 regulates HERG K+ channels by decelerating deactivation. However, little is known about how ginsenoside metabolites regulate HERG K+ channel activity. In the present study, we examined the effects of ginsenoside metabolites such as compound K (CK), protopanaxadiol (PPD), and protopanaxatriol (PPT) on HERG K+ channel activity by expressing human α subunits in Xenopus oocytes. CK induced a large persistent deactivating-tail current (Ideactivating-tail) and significantly decelerated deactivating current decay in a concentration-dependent manner. The EC50 for persistent Ideactivating-tail was 16.6±1.3 μM. In contrast to CK, PPT accelerated deactivating-tail current deactivation. PPD itself had no effects on deactivating-tail currents, whereas PPD inhibited ginsenoside Rg3-induced persistent Ideactivating-tail and accelerated HERG K+ channel deactivation in a concentration-dependent manner. These results indicate that ginsenoside metabolites exhibit differential regulation on Ideactivating-tail of HERG K+ channel.