Seok Choi

Suppressive Effect of Astaxanthin Isolated from the Xanthophyllomyces dendrorhous Mutant on Ethanol-Induced Gastric Mucosal Injury in Rats

Ethanol has been found to induce ulcerative gastric lesion in humans. The present study investigated the in vivo protective effect of astaxanthin isolated from the Xanthophyllomyces dendrorhous mutant against ethanol-induced gastric mucosal injury in rats. The rats were treated with 80% ethanol for 3 d after pretreatment with two doses of astaxanthin (5 and 25 mg/kg of body weight respectively) for 3 d, while the control rats received only 80% ethanol for 3 d. The oral administration of astaxanthin (5 and 25 mg/kg of body weight) showed significant protection against ethanol-induced gastric lesion and inhibited elevation of the lipid peroxide level in gastric mucosa. In addition, pretreatment with astaxanthin resulted in a significant increase in the activities of radical scavenging enzymes such as superoxide dismutase, catalase, and glutathione peroxidase. A histologic examination clearly indicated that the acute gastric mucosal lesion induced by ethanol nearly disappeared after pretreatment with astaxanthin.

Characteristics of Gintonin-Mediated Membrane Depolarization of Pacemaker Activity in Cultured Interstitial Cells of Cajal

Background/Aims: Ginseng regulates gastrointestinal (GI) motor activity but the underlying components and molecular mechanisms are unknown. We investigated the effect of gintonin, a novel ginseng-derived G protein-coupled lysophosphatidic acid (LPA) receptor ligand, on the pacemaker activity of the interstitial cells of Cajal (ICC) in murine small intestine and GI motility. Materials and Methods: Enzymatic digestion was used to dissociate ICC from mouse small intestines. The whole-cell patch-clamp configuration was used to record pacemaker potentials and currents from cultured ICC in the absence or presence of gintonin. In vivo effects of gintonin on gastrointestinal (GI) motility were investigated by measuring the intestinal transit rate (ITR) of Evans blue in normal and streptozotocin (STZ)-induced diabetic mice. Results: We investigated the effects of gintonin on pacemaker potentials and currents in cultured ICC from mouse small intestine. Gintonin caused membrane depolarization in current clamp mode but this action was blocked by Ki16425, an LPA1/3 receptor antagonist, and by the addition of GDPβS, a GTP-binding protein inhibitor, into the ICC. To study the gintonin signaling pathway, we examined the effects of U-73122, an active PLC inhibitor, and chelerythrine and calphostin, which inhibit PKC. All inhibitors blocked gintonin actions on pacemaker potentials, but not completely. Gintonin-mediated depolarization was lower in Ca2+-free than in Ca2+-containing external solutions and was blocked by thapsigargin. We found that, in ICC, gintonin also activated Ca2+-activated Cl- channels (TMEM16A, ANO1), but not TRPM7 channels. In vivo, gintonin (10-100 mg/kg, p.o.) not only significantly increased the ITR in normal mice but also ameliorated STZ-induced diabetic GI motility retardation in a dose-dependent manner. Conclusions: Gintonin-mediated membrane depolarization of pacemaker activity and ANO1 activation are coupled to the stimulation of GI contractility through LPA1/3 receptor signaling pathways in cultured murine ICC. Gintonin might be a ingredient responsible for ginseng-mediated GI tract modulations, and could be a novel candidate for development as a prokinetic agent that may prevent or alleviate GI motility dysfunctions in human patients.

Effects of Ginsenosides on Carbachol-Stimulated Formation of Inositol Phosphates in Rat Cortical Cell Cultures

We examined the effect of ginseng total saponins (GTS) on phosphoinositide metabolism stimulated by activation of muscarinic receptor using rat cortical cultures. Carbachol stimulated formation of [3H]inositol phosphates ([3H]InsPs) by 3.3-fold over basal level in [3H]inositol-prelabeled cells. Pretreatment of GTS inhibited formation of [3H]InsPs evoked by carbachol by 70%–90%. Addition of GTS alone had no effect on the basal formation of [3H]InsPs. The inhibitory effect of the GTS on carbachol-stimulated formation of [3H]InsPs was dose- and time-dependent. IC50 was 6.0 ± 2.8 μg/ml. We also examined the effect of GTS on [3H]InsP1, [3H]InsP2, or [3H]InsP3 formation evoked by carbachol. Although GTS had no effect on the basal [3H]InsP1, [3H]InsP2, or [3H]InsP3 formation, pretreatment of GTS inhibited [3H]InsP1, [3H]InsP2, or [3H]InsP3 formation evoked by carbachol, respectively. Addition of individual ginsenosides such as ginsenoside Rb1, Rc, Rd, Re, or Rg2 had no effect on the basal formation of [3H]InsPs, whereas pretreatment of ginsenoside Rb2, Rc, Rd, Re, Rf, Rg1 or Rg2 inhibited formation of [3H]InsPs evoked by carbachol by 79%–89%. The results suggest that the inhibitory effect of GTS and its individual ginsenosides on carbachol-stimulated formation of [3H]InsPs in cortical neurons could be one pharmacological action of Panax ginseng.

Regulatory Roles of Endogenous Mitogen-Activated Protein Kinases and Tyrosine Kinases in the Pacemaker Activity of Colonic Interstitial Cells of Cajal

Background and Purpose: Mitogen-activated protein (MAP) and tyrosine kinases play an important role in regulating smooth muscle contraction of the gastrointestinal (GI) tract. Interstitial cells of Cajal (ICCs) are pacemaker cells that regulate GI smooth muscle activity. Thus, the role of MAP and tyrosine kinases on the pacemaker potentials of colonic ICCs was investigated. Methods: Cultured ICCs were prepared from mice colons, and their pacemaker potentials were recorded using whole-cell patch clamping. Results: In current-clamping mode, colonic ICCs displayed spontaneous pacemaker potentials. SB203580 (a p38 MAP kinase inhibitor), SP600125 (a c-jun NH2-terminal kinase (JNK) inhibitor), genistein and herbimycin A (tyrosine kinase inhibitors) blocked the generation of pacemaker potentials. However, PD98059 (a p42/44 MAP kinase inhibitor) had no effects on pacemaker potentials. LY-294002 (phosphoinositide 3-kinase inhibitor) also reduced the pacemaker potential frequency but calphostin C and chelerythrine (protein kinase C inhibitors) had no effects. However, PD98059, SB203589, SP600125, genistein, herbimycin A, LY-294002, and calphostin C had no effect on normal pacemaker activity in small intestinal ICCs. Conclusions: Endogenous p38 MAP kinases, JNKs, tyrosine kinases, and PI3-kinases participate in the generation of pacemaker potentials in colonic ICCs but not in ICCs of the small intestine.

Regulation of the Pacemaker Activity of Colonic Interstitial Cells of Cajal by Protease-Activated Receptors: Involvement of Hyperpolarization-Activated Cyclic Nucleotide Channels

Background and Purpose: The exact mechanism of protease-activated receptors (PARs) on pacemaker activity of interstitial cells of Cajal (ICCs) has not been reported. We investigated the effects on pacemaker activity by the activation of PARs and its signal mechanisms in colonic ICCs. Methods: The whole-cell patch-clamp technique, RT-PCR and Ca2+ imaging were used in cultured ICCs from mouse colon. Results: PAR-1 and PAR-2 were expressed in Ano-1 positive ICCs. TFLLR-NH2 (a PAR-1 agonist) and trypsin (a PAR-2 agonist) depolarized the membrane and increased the pacemaker potential frequency. U-73122 (a phospholipase C (PLC) inhibitor) and thapsigargin (a Ca2+ ATPase inhibitor) suppressed the TFLLR-NH2- and trypsin-induced effects on pacemaker potential. TFLLR-NH2 and trypsin also increased intracellular Ca2+ ([Ca2+]i) intensity with increasing of Ca2+ oscillations. Genistein (a tyrosine kinase inhibitor), SP600125 (a JNK inhibitor), CsCl, ZD7288, clonidine (hyperpolarization-activated cyclic nucleotide (HCN) channel blockers), SQ-22536 and dideoxyadenosine (adenylate cyclase inhibitors) suppressed the increased pacemaker potential frequency without effects on depolarization of the membrane induced by TFLLR-NH2 and trypsin. Conclusion: These results suggest that activation of PAR-1 and PAR-2 modulates the pacemaker activity of colonic ICCs through the PLC-dependent [Ca2+]i release pathway. The increased pacemaker potential frequency by PAR-1 and PAR-2 was also dependent on tyrosine kinase, JNK, and HCN activation.