Toshio Miyase

Formation of antioxidants from (-)-epigallocatechin gallate in mild alkaline fluids, such as authentic intestinal juice and mouse plasma.

The oxidative dimerization of (-)-epigallocatechin gallate (EGCG), the major catechin of tea leaves (Camellia sinensis L.), in authentic intestinal juice (pH 8.5) and mouse plasma (pH 7.8) was investigated. EGCG was unstable in the alkaline solutions over pH 7.4. The content of EGCG was decreased to 19.4% and 60.7% at 5 minutes in the intestinal juice and plasma, respectively. Three products-P-1 (theasinensin A), P-2 (a new dimerized product reported in a previous paper), and P-3 (theasinensin D, a rotational isomer of P-1)-were detected in these fluids. The sum of the molar contents of the three products formed after 5 minutes of incubation at 37 degrees C corresponded to 35.1% and 21.9% of the degraded molar content of EGCG, respectively. These dimerization products of EGCG would be formed by the dehydrogenation and decarboxylation of EGCG under oxidative conditions in alkaline solutions. The formation of P-2 was greater than that of P-1 and of P-3 at 30 minutes of incubation in the intestinal juice and mouse plasma. Fe(2+)-chelating activities of the three products were much higher than that of EGCG, and superoxide anion radical-scavenging activity of P-2 was also significantly higher than that of EGCG. The absorbance of P-2 administered to male ddY mice was studied. The content of P-2 in mouse plasma was less than that of administration of EGCG, but P-2 was absorbed quickly within 30 minutes and metabolized slowly. These dimerization products of EGCG are expected to contribute to in vivo antioxidative activities enhanced by tea drinking.

O-methylated catechins from tea leaves inhibit multiple protein kinases in mast cells.

Tea contains a variety of bioactive compounds. In this study, we show that two O-methylated catechins, (-)-epigallocatechin-3-O-(3-O-methyl) gallate and (-)-epigallocatechin-3-O-(4-O-methyl) gallate, inhibit in vivo mast cell-dependent allergic reactions more potently than their nonmethylated form, (-)-epigallocatechin-3-O-gallate. Consistent with this, these O-methylated catechins inhibit IgE/Ag-induced activation of mouse mast cells: histamine release, leukotriene release, and cytokine production and secretion were all inhibited. As a molecular basis for the catechin-mediated inhibition of mast cell activation, Lyn, Syk, and Bruton’s tyrosine kinase, the protein tyrosine kinases, known to be critical for early activation events, are shown to be inhibited by the O-methylated catechins. In vitro kinase assays using purified proteins show that the O-methylated catechins can directly inhibit the above protein tyrosine kinases. These catechins inhibit IgE/Ag-induced calcium response as well as the activation of downstream serine/threonine kinases such as Akt and c-Jun N-terminal kinase. These observations for the first time have revealed the molecular mechanisms of antiallergic effects of tea-derived catechins.

Simultaneous determination of twelve tea catechins by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method with electrochemical detection was developed for the determination of twelve tea catechins including four major catechins: epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG); four of their epimers at the C-2 position, C, GC, CG and GCG; and four methylated catechin derivatives, epigallocatechin-3-O-(3-O-methyl)gallate, gallocatechin-3-O-(3-O-methyl)gallate, epigallocatechin-3-O-(4-O-methyl)gallate and epicatechin-3-O-(3-O-methyl)gallate. These catechins were separated on an ODS C18 reversed-phase column by isocratic elution with 0.1 M NaH2PO4 buffer (pH 2.5)-acetonitrile (87:13) containing 0.1 mM EDTA.2Na. The detection limits (S/N = 3) of these catechins were approximately 10-40 pmol ml-1 at an applied voltage of 600 mV. Extracting these catechins from tea leaf powder with H2O-acetonitrile (1:1) at 30 degrees C for 40 min inhibited the epimerization at C-2 significantly from these epicatechins compared to extraction with hot water at 90 degrees C. This analytical method is sensitive to and appropriate for the simultaneous determination of various biologically active catechins in green tea.

Ionone and lignan glycosides from Epimedium diphyllum

Abstract From the aerial parts of Epimedium diphyllum, a new ionone derivative glucoside, icariside B8, two new lignan glycosides, icarisides E4 and E5 and a new phenylethanoid glucoside, icariside D2, have been isolated together with 20 known compounds. The structures of four new compounds were established by spectral and chemical evidence.

Phenylethanoid glycosides from Stachys officinalis

From the aerial parts of Stachys officinalis, six new phenylethanoid glycosides, named betonyosides A-F, and six known phenylethanoid glycosides, acetoside, acetoside isomer, campneosides II, forsythoside B and leucosceptoside B, were isolated and their structures were elucidated from spectroscopic and chemical evidence. Campneosides II were separated into two epimers.

Phenylethanoid glycosides from Plantago asiatica

Abstract Six new phenylethanoid glycosides, plantainosides A–F, were isolated from a water extract of the whole plants of Plantago asiatica together with eight known phenylethanoid glycosides. Their structures were determined on the basis of chemical and spectral evidence.

Lignan and terpene glycosides from Epimedium sagittatum

From the aerial parts of Epimedium sagittatum, four new lignans, icarisides E6, E7, icariols A1, A2, a new phenylethanoid, icariside D3, a new phenylpropanoid, icariside H1 and a new ionone derivative, icariside B9, have been isolated together with 20 known compounds. The structures of new compounds were established by spectral and chemical evidence.

Terpenic glycosides from Pluchea indica

Abstract Investigation of the aerial parts of Pluchea indica afforded five new terpenic glycosides, linaloyl glucoside, linaloyl apiosyl glucoside, 9-hydroxylinaloyl glucoside, plucheosides A and B, in addition to 15 known compounds. The structures of new compounds were elucidated on the basis of chemical and spectral data.

Antioxidants from Lespedeza homoloba. (I)

The stems of Lespedeza homoloba yielded eight new and three known phenolic compounds. Their structures have been elucidated on the basis of their spectral data. These compounds had strong antioxidative activity against lipid peroxidation in the rat brain homogenate test. 3,9-Dihydroxypterocarp-6a-en and lespedezol A2 showed significant antiallergic activity in allergic (type I) mice.

Phenylethanoid and lignan glycosides from Verbascum thapsus.

Verbascum thapsus afforded, in addition to three known phenylethanoid glycosides and four lignan ones, five new phenylethanoid glycosides and one new lignan glycoside. Structures of the compounds were elucidated by spectroscopic methods and chemical evidence.