Toshio Morikawa

Absolute stereostructure of potent α-glucosidase inhibitor, salacinol, with unique thiosugar sulfonium sulfate inner salt structure from Salacia reticulata

A most potent alpha-glucosidase inhibitor named salacinol has been isolated from an antidiabetic Ayurvedic traditional medicine, Salacia reticulata WIGHT, through bioassay-guided separation. The absolute stereostructure of salacinol was determined on the basis of chemical and physicochemical evidence, which included the alkaline degradation of salacinol to 1-deoxy-4-thio-D-arabinofuranose and the X-ray crystallographic analysis, to be the unique spiro-like configuration of the inner salt comprised of 1-deoxy-4-thio-D-arabinofuranosyl sulfonium cation and 1-deoxy-D-erythrosyl-3-sulfate anion. Salacinol showed potent inhibitory activities on several alpha-glucosidases, such as maltase, sucrase, and isomaltase, and the inhibitory effects on serum glucose levels in maltose- and sucrose-loaded rats (in vivo) were found to be more potent than that of acarbose, a commercial alpha-glucosidase inhibitor.

Inhibitory effect and action mechanism of sesquiterpenes from zedoariae rhizoma on D-galactosamine / lipopolysaccharide-induced liver injury

Hepatoprotective sesquiterpenes were isolated from the aqueous acetone extract of Zedoariae Rhizoma, the rhizome of Curcuma zedoaria ROSCOE (Zingiberaceae). Principal sesquiterpenes, furanodiene, germacrone, curdione, neocurdione, curcumenol, isocurcumenol, aerugidiol, zedoarondiol, and curcumenone and curcumin were found to show potent protective effect on D-galactosamine (D-GalN)/lipopolysaccharide (LPS)-induced acute liver injury in mice. Plausible action mechanisms for their hepatoprotective activity were clarified on the basis of the inhibitory effect on D-GalN-induced cytotoxicity in primary cultured rat hepatocytes, LPS-induced NO production in cultured mouse peritoneal macrophages, and D-GalN/tumor necrosis factor-alpha (TNF-alpha)-induced liver injury in mice.

Antioxidant constituents from rhubarb : Structural requirements of stilbenes for the activity and structures of two new anthraquinone glucosides

The methanolic extracts from five kinds of rhubarb were found to show scavenging activity for DPPH radical and .O2-. Two new anthraquinone glucosides were isolated from the rhizome of Rheum undulatum L. together with two anthraquinone glucosides, a naphthalene glucoside, and 10 stilbenes. In the screening test for radical scavenging activity of rhubarb constituents, stilbenes and a naphthalene glucoside showed activity, but anthraquinones and sennosides did not. In addition, most stilbenes inhibited lipid peroxidation of erythrocyte membrane by tert-butyl hydroperoxide. Detailed examination of the scavenging effect on various related compounds suggested the following structural requirements; 1) phenolic hydroxyl groups are essential to show the activity; 2) galloyl moiety enhances the activity; 3) glucoside moiety reduces the activity; 4) dihydrostilbene derivatives maintain the scavenging activity for the DPPH radical, but they show weak activity for .O2-. In addition, several stilbenes with both the 3-hydroxyl and 4-methoxyl groups inhibited xanthine oxidase.

Phytoestrogens from the roots of Polygonum cuspidatum (Polygonaceae): structure-requirement of hydroxyanthraquinones for estrogenic activity.

The methanolic extract from the roots of Polygonum (P.) cuspidatum was found to enhance cell proliferation at 30 or 100 microg/mL in MCF-7, an estrogen-sensitive cell line. By bioassay-guided separation from P. cuspidatum with the most potent activity, emodin and emodin 8-O-beta-D-glucopyranoside were isolated as active principles. The methanolic extracts from Polygonum, Cassia, Aloe, and Rheum species, which were known to contain anthraquinones, also showed the MCF-7 proliferation. As a result of the evaluation of various anthraquinones from plant sources and synthetic anthraquinones, aloe-emodin, chrysophanol, chrysophanol 8-O-beta-D-glucopyranoside, and 1,8-dihydroxyanthraquinone showed weak activity. On the other hand, alizalin and 2,6-dihydroxyanthraquinone as well as emodin having the 2- and/or 6-hydroxyl groups showed potent activity. These results show that the unchelated hydroxyl group is essential for strong activity. Emodin and 2,6-dihydroxyanthraquinone also inhibited 17beta-estradiol binding to human estrogen receptors (ERs) with K(i) values of 0.77 and 0.31microM for ERalpha and 1.5 and 0.69 microM for ERbeta. These findings indicate that hydroxyanthraquinones such as emodin are phytoestrogens with an affinity to human estrogen receptors.

Structural requirements of flavonoids for inhibition of antigen-Induced degranulation, TNF-α and IL-4 production from RBL-2H3 cells

To clarify the structure-activity relationships of flavonoids for antiallergic activity, the inhibitory effects of various flavonoids on the release of beta-hexosaminidase, as a marker of degranulation of RBL-2H3 cells, were examined. Among them, luteolin (IC(50)=3.0 microM), diosmetin (2.1 microM), and fisetin (3.0 microM) were found to show potent inhibitory activity, and the results suggested the following structural requirements of flavonoids: (1) the 2-3 double bond of flavones and flavonols is essential for the activity; (2) the 3- or 7-glycoside moiety reduced the activity; (3) as the hydroxyl groups at the 3-, 4-, 5-, 6-, and 7-positions increased in number, the inhibitory activities become stronger; (4) the flavonols with a pyrogallol type moiety (the 3,4,5-trihydroxyl groups) at the B ring exhibited less activity than those with a phenol type moiety (the 4-hydroxyl group) or catechol type moiety (the 3,4-dihydroxyl groups) at the B ring; (5) the activities of flavones were stronger than those of flavonols; and (6) methylation of flavonols at the 3-position reduced the activity. However, (7) several flavones and flavonols with the 4- and/or 7-methoxyl groups did not obey rules (3), (4), and (5). In addition, several flavonoids, that is apigenin, luteolin, diosmetin, fisetin, and quercetin, inhibited the antigen-IgE-mediated TNF-alpha and IL-4 production from RBL-2H3 cells, both of which participate in the late phase of type I allergic reactions.

Effects of stilbene constituents from rhubarb on nitric oxide production in lipopolysaccharide-activated macrophages

Two new anthraquinone glucosides [chrysophanol 8-O-beta-D-(6-galloyl)-glucopyranoside, aloe-emodin 1-O-beta-D-glucopyranoside] together with various known stilbenes and their glucosides, anthraquinone glucosides, and a naphthalene glucoside were isolated from the rhizome of Rheum undulatum L. Three stilbenes (rhapontigenin, piceatannol, resveratrol), a naphthalene glucoside (torachrysone 8-O-beta-D-glucopyranoside), and two stilbene glucoside gallates (rhaponticin 2-O-gallate, rhaponticin 6-O-gallate) showed inhibitory activity of NO production in lipopolysaccharide-activated macrophages, (IC50 = 11-69 microM). The oxygen functions (-OH,-OCH3) at the benzene ring were found to be essential to show the activity. Whereas, the glucoside moiety reduced the activity, while the alpha,beta-double bond did not affect the activity. Furthermore, the active stilbenes (rhapontigenin, piceatannol, resveratrol) inhibited iNOS induction.

Inhibitory effects of sesquiterpenes from bay leaf on nitric oxide production in lipopolysaccharide-activated macrophages: structure requirement and role of heat shock protein induction.

The methanolic extract from the leaves of Laurus nobilis (bay leaf, laurel) was found to inhibit nitric oxide (NO) production in lipopolysaccharide (LPS)-activated mouse peritoneal macrophages. Through bioassay-guided separation, fourteen known sesquiterpenes were isolated from the active fraction and were examined for ability to inhibit the NO production. Seven sesquiterpene lactones (costunolide, dehydrocostus lactone, eremanthine, zaluzanin C, magnolialide, santamarine and spirafolide) potently inhibited LPS-induced NO production (IC50 = 1.2 approximately 3.8 microM). Other sesquiterpene constituents also showed the inhibitory activity (IC50 > or = 21 microM), but their inhibitory activities were less than those of sesquiterpene lactones. Alpha-methylene-gamma-butyrolactone also showed inhibitory activity (IC50 = 9.6 microM), while mokko lactone and watsonol A etc., reductants of the alpha-methylene-gamma-butyrolactone moiety by NaBH4 or DIBAL, and a 2-mercaptoethanol adduct of dehydrocostus lactone showed little activity (IC50 > or = 18 microM). These results indicated that the alpha-methylene-gamma-butyrolactone moiety is important for the activity. Furthermore, costunolide and dehydrocostus lactone inhibited inducible nitric oxide synthase (iNOS) induction in accordance with induction of heat shock protein 72 (HSP 72). These results suggested that, as one of their mechanisms of action, sesquiterpene lactones induce HSP 72 thereby preventing nuclear factor-kappaB activation followed by iNOS induction.

Gastroprotective effects of phenylpropanoids from the rhizomes of Alpinia galanga in rats: structural requirements and mode of action

The effects of 1S-1-acetoxychavicol acetate and related phenylpropanoids isolated from the rhizomes of Alpinia galanga on ethanol-induced gastric lesions in rats were examined. Among them, 1S-1-acetoxychavicol acetate and 1S-1-acetoxyeugenol acetate markedly inhibited the ethanol-induced gastric mucosal lesions (ED(50)=0.61 and ca. 0.90 mg/kg). In addition, 1S-1-acetoxychavicol acetate inhibited the lesions induced by 0.6 M HCl (ED(50)=0.73 mg/kg) and aspirin (ED(50)=0.69 mg/kg) but it did not show a significant effect on indomethacin-induced gastric lesions and acid output in pylorus-ligated rats at doses of 0.5-5.0 mg/kg. From the gastroprotective effects of various related compounds, the 1-acetoxyl group of 1S-1-acetoxychavicol acetate and 1S-1-acetoxyeugenol acetate was found to be essential for their strong activity. With regard to the mode of action, the gastroprotective effects of 1S-1-acetoxychavicol acetate were attenuated by pretreatment with indomethacin and N-ethylmaleimide, and 1S-1-acetoxychavicol acetate significantly increased the glutathione levels of gastric mucosa in rats. These findings suggest that endogenous prostaglandins and sulfhydryl compounds are involved in the protective effect of 1S-1-acetoxychavicol acetate.

Antiallergic principles from Alpinia galanga: Structural requirements of phenylpropanoids for inhibition of degranulation and release of TNF-α and IL-4 in RBL-2H3 cells

The 80% aqueous acetone extract of the rhizomes of Alpinia galanga was found to inhibit release of beta-hexosaminidase, as a marker of antigen-IgE-mediated degranulation in RBL-2H3 cells. Nine known phenylpropanoids and p-hydroxybenzaldehyde were isolated from the extract. Among them, 1S-1-acetoxychavicol acetate and 1S-1-acetoxyeugenol acetate exhibited potent inhibitory activity with IC(50) values of 15 and 19 microM. From the effects of various related compounds, both the 1- and 4-acetoxyl groups of 1S-1-acetoxychavicol acetate and 1S-1-acetoxyeugenol acetate were essential for their strong activity, and the 2-3 double bond enhanced the activity. In addition, 1S-1-acetoxychavicol acetate and 1S-1-acetoxyeugenol acetate inhibited ear passive cutaneous anaphylaxis reactions in mice and the antigen-IgE-mediated TNF-alpha and IL-4 production, both of which participate in the late phase of type I allergic reactions, in RBL-2H3 cells.

Antidiabetogenic constituents from several natural medicines

In the course of our studies on antidiabetogenic and antidiabetic principles of natural medicines and medicinal foodstuffs, we have isolated salacinol and kotalanol with unique thiosugar sulfonium sulfate inner salt structures from the antidiabetic Ayurvedic traditional medicines, Salacia reticulata and S. oblonga. Salacinol and kotalanol showed potent inhibitory activities against intestinal α-glucosidase, and also inhibitory effects of salacinol on the increase in serum glucose levels in maltose- and sucrose-loaded rats were found to be more potent than those of acarbose. In addition, various flavonoids with potent inhibitory activities against rat lens aldose reductase such as quercitrin desmanthin-1 and guaijaverin were isolated from Myrcia multiflora and several natural medicines, and some structural requirements of flavonoids for aldose reductase inhibitory activity were clarified.