Inhibitory effect of nordihydroguaiaretic acid, a plant lignan, on Helicobacter pylori-associated gastric carcinogenesis in Mongolian gerbils.

Recent epidemiological studies have demonstrated that consumption of certain natural products can lower cancer risk in humans. For example, plant-derived lignans have been shown to exert chemopreventive effects against cancer in vitro and in vivo. In the present study, the effects of three such lignans, termed arctiin, arctigenin, and nordihydroguaiaretic acid (NDGA), on the proliferation of Helicobacter pylori and the prevention of H. pylori-associated gastric cancer were investigated in Mongolian gerbils. To examine the effects of arctigenin and NDGA on stomach carcinogenesis, specific pathogen-free male, 5-week-old gerbils were infected with H. pylori, administered 10 p.p.m. N-methyl-N-nitrosourea in their drinking water and fed diets containing various concentrations of lignans until they were killed after 52 weeks. At a dietary level of 0.25%, NDGA significantly decreased the incidence of gastric adenocarcinomas. Arctigenin, in contrast, failed to attenuate neoplasia at a level of 0.1%. Both NDGA and arctigenin significantly reduced serum 8-hydroxy-2'-deoxyguanosine levels at doses of 0.25 and 0.05% (NDGA), and 0.1% (arctigenin). Administration of 0.25% NDGA significantly suppressed the formation of intestinal metaplasia both in the antrum and the corpus. Although all three lignans dose-dependently inhibited the in vitro proliferation of H. pylori, there were no differences in the titers of anti-H. pylori antibodies or the amount of the H. pylori-specific urease A gene among all H. pylori-infected groups. These results suggest that NDGA might be effective for prevention of gastric carcinogenesis. The possible mechanisms appear to be related to inhibitory effects on progression of gastritis and antioxidative activity rather than direct antimicrobial influence.

Quantification of a broad spectrum of lignans in cereals, oilseeds, and nuts.

Twenty-four plant lignans were analyzed by high-performance liquid chromatography-tandem mass spectrometry in bran extracts of 16 cereal species, in four nut species, and in two oilseed species (sesame seeds and linseeds). Eighteen of these were lignans previously unidentified in these species, and of these, 16 were identified in the analyzed samples. Four different extraction methods were applied as follows: alkaline extraction, mild acid extraction, a combination of alkaline and mild acid extraction, or accelerated solvent extraction. The extraction method was of great importance for the lignan yield. 7-Hydroxymatairesinol, which has not previously been detected in cereals because of destructive extraction methods, was the dominant lignan in wheat, triticale, oat, barley, millet, corn bran, and amaranth whole grain. Syringaresinol was the other dominant cereal lignan. Wheat and rye bran had the highest lignan content of all cereals; however, linseeds and sesame seeds were by far the most lignan-rich of the studied species.

Endothelium-dependent vascular relaxation induced by Eucommia ulmoides Oliv. bark extract is mediated by NO and EDHF in small vessels.

The vasorelaxant effects of the aqueous extract prepared from the bark of the Chinese medicinal herb, Eucommia ulmoides Oliv. (also referred to as Tu-Chung or Du-Zhong), which is a common active ingredient in traditional antihypertensive herbal prescriptions in China, have recently been characterized in rat aorta and dog carotid artery. The vasorelaxant effect of eucommia bark extract on these large elastic arteries was found to be entirely endothelium-dependent and nitric oxide (NO)-mediated. Since smaller muscular arteries play a more dominant role in the change of peripheral resistance and thus the regulation of blood pressure, we have now compared the relaxant effects of eucommia bark extract using aorta and the proximal as well as the distal ends of the superior mesenteric arteries from the rat, with a specific objective to investigate whether smaller muscular arteries also elicit endothelium-dependent vascular relaxation (EDVR) in response to eucommia bark extract. We have also determined whether the EDVR, if indeed occurring in the mesenteric arteries, is mediated entirely by NO, or whether it also involves endothelium-derived hyperpolarizing factor (EDHF). We found that all three types of vessel preparations elicit EDVR in response to the eucommia bark extract concentration-dependently in a similar manner to the relaxant responses to carbachol (CCh). Although the NO synthase inhibitor L-NAME totally abolished the EDVR in aorta, it only partial abolished EDVR in mesenteric arteries isolated from each end, the distal end being more resistant to L-NAME. However, the residual L-NAME-resistant relaxation of the rat mesenteric arteries could be further inhibited by preincubation of the vessels with the combination of L-NAME and 15-20 mM KCl (KCl itself at this low concentration caused little or no contraction). Therefore, the EDVR induced by the eucommia extract and CCh in aorta is mediated entirely by NO, and that in mesenteric arteries by NO as well as EDHF, with the EDHF component (inhibited by KCl) larger in the smaller distal end of the rat mesenteric artery. Results of our study offer a plausible mechanistic basis for the vasorelaxing action of Eucommia ulmoides Oliv., which may account for its well-documented antihypertensive action.

Vascular effects of Siberian ginseng (Eleutherococcus senticosus): endothelium-dependent NO- and EDHF-mediated relaxation depending on vessel size.

Siberian ginseng (SG) has been widely and historically consumed as a health food product for the improvement of self well-being, but whether vascular relaxation may contribute to such a therapeutic health effect has not been studied. We therefore investigated the vasorelaxant effect of the aqueous extract of the roots of SG (Eleutherococcus senticosus Maxim) using several in vitro vascular rings prepared from dog carotid artery, rat aorta and rat mesenteric artery. SG extract (0.04-0.8 mg/ml) caused concentration-dependent relaxation in dog carotid arterial rings pre-contracted with 100 microM phenylephrine (PE), and the relaxation was primarily endothelium-dependent. Treatment with 100 microM L-NOARG (a nitric oxide synthase inhibitor) either prevented or totally reverted SG-induced relaxation, suggesting that the endothelium-dependent relaxation was mediated by NO. Similar endothelium-dependent vascular relaxant responses were also obtained with rat aortic and mesenteric arterial rings, except that it occurred over a relatively higher concentration range of SG (0.5-2.0 mg/ml). When tested in the presence of 300 microM L-NAME, the vasorelaxant effect of SG was inhibited totally in rat aorta but only partially in rat mesenteric artery. The relaxation to SG that was insensitive to L-NAME in rat mesenteric arterial rings was eliminated when the rings (both proximal and distal ends) were pre-treated with a combination of 300 microM L-NAME and 15 mM KCl indicating the involvement of endothelium-derived hyperpolarizing factor (EDHF). This vasorelaxant response of the SG extract was inhibited partially by atropine (1 microM), completely by TEA (5 mM), but not by indomethacin (1 microM) or propranolol (10 microM). SG up to 2 mg/ml had no effect on KCl-induced contraction in any of the vascular rings studied. When compared with carbachol-induced (CCh) relaxation, SG resembles CCh in that the sensitivity to L-NAME inhibition is dependent on vascular size, i.e. aorta >proximal end of mesenteric artery >distal end of mesenteric artery. However, SG exhibited different potencies to relaxation while CCh showed similar potency (EC(50) of about 0.2 microM) in all three vascular segments. In conclusion, we have demonstrated that the vascular effect of SG is endothelium-dependent and mediated by NO and/or EDHF depending on the vessel size. Other vasorelaxation pathways, such as inhibition of K(+)-channels and activation of muscarinic receptors, may also be involved.

Endothelium-dependent vasorelaxant effects of the aqueous extracts of the Eucommia ulmoides Oliv. leaf and bark: implications on their antihypertensive action.

The vascular effects of three extract preparations from the Chinese medicinal herb, Eucommia ulmoides Oliv., which is historically an active ingredient commonly used in antihypertensive herbal prescriptions in China, were investigated with isometric contraction using isolated rat aortic and dog carotid rings. Both aqueous extracts isolated from eucommia leaf (L) and bark (B) concentration dependently caused endothelium-dependent relaxation in vessels precontracted with 1 microM phenylephrine (PE), but the methanol extract of the leaf (M) had no effect. Vessels precontracted with KCl and de-endothelialized vessels precontracted with PE were not affected by B or L. The endothelium-dependent relaxation evoked by B and L was either abolished or substantially inhibited by NG-nitro-L-arginine methyl ester (L-NAME) and methylene blue (MB), indicating the involvement of the nitric oxide (NO) synthase pathway in the vasorelaxant action of B and L. The relaxation to the aqueous extract of eucommia bark was not inhibited with 1 microM atropine, but was inhibited by 3-5 mM tetraethylammonium (TEA) and 3 mM 4-aminopyridine. This suggests that the endothelium-dependent, NO-mediated relaxation evoked by the aqueous eucommia extracts was not mediated via the activation of endothelium muscarinic receptors and may involve the activation of K+ -channels. Results in this study have provided the first evidence on the in vitro vasorelaxant action of E. ulmoides Oliv. that forms the pharmacological basis for its well-documented antihypertensive action.

Plant lignans in soy-based health supplements.

The presence of plant lignans in 14 different soy-based health supplements is reported here for the first time together with the analysis of the isoflavone content, for which these products are commercialized. Six plant lignans, i.e., secoisolariciresinol, matairesinol, syringaresinol, lariciresinol, isolariciresinol, and pinoresinol, have been identified and quantified by gas chromatography-mass spectrometry, and a positive correlation has been found between the levels of plant lignans and the levels of isoflavones in the different products. Additional quantification of plant lignans and isoflavones in soybeans has been carried out, and results are provided to allow the comparison of the average levels in soybeans and soy-based supplements.

Pharmacognostical studies of cistanchis herba (III) phylogenetic relationship of the cistanche plants based on plastid rps2 gene and rpl16-rpl14 intergenic spacer sequences.

The phylogenetic relationship of Cistanche deserticola, C. salsa and C. tubulosa was analyzed by comparing the nucleotide sequences of the plastid rps2 gene and the intergenic spacer region between rpl16 and rpl14. By comparison of sequence data, the Cistanche samples were distinguishable from each other. The results were consistent with their anatomical and chemical characteristics. Intraspecific variations were found in C. salsa and C. tubulosa among the geographical populations. The NJ tree reconstructed based on the sequence data revealed that C. deserticola and C. salsa from China were closely related to each other, and C. tubulosa was placed as an outgroup of them.

Biotransformation of pinoresinol diglucoside to mammalian lignans by human intestinal microflora, and isolation of Enterococcus faecalis strain PDG-1 responsible for the transformation of (+)-pinoresinol to (+)-lariciresinol.

By anaerobic incubation of pinoresinol diglucoside (1) from the bark of Eucommia ulmoides with a fecal suspension of humans, eleven metabolites were formed, and their structures were identified as (+)-pinoresinol (2), (+)-lariciresinol (3), 3'-demethyl-(+)-lariciresinol (4), (-)-secoisolariciresinol (5), (-)-3-(3", 4"-dihydroxybenzyl)-2-(4'-hydroxy-3'-methoxybenzyl)butane-1, 4-diol (6), 2-(3', 4'-dihydroxybenzyl)-3-(3", 4"-dihydroxybenzyl)butane-1, 4-diol (7), 3-(3"-hydroxybenzyl)-2-(4'-hydroxy-3'-methoxybenzyl)butane-1, 4-diol (8), 2-(3', 4'-dihydroxybenzyl)-3-(3"-hydroxybenzyl)butane-1, 4-diol (9), (-)-enterodiol (10), (-)-(2R, 3R)-3-(3", 4"-dihydroxybenzyl)-2-(4'-hydroxy-3'-methoxybenzyl)butyrolactone (11), (-)-(2R, 3R)-2-(3', 4'-dihydroxybenzyl)-3-(3", 4"-dihydroxybenzyl)butyrolactone (12), (-)-(2R, 3R)-3-(3"-hydroxybenzyl)-2-(4'-hydroxy-3'-methoxybenzyl)butyrolactone (13), 2-(3', 4'-dihydroxybenzyl)-3-(3"-hydroxybenzyl)butyrolactone (14), 2-(3'-hydroxybenzyl)-3-(3", 4"-dihydroxybenzyl)butyrolactone (15) and (-)-(2R, 3R)-enterolactone (16) by various spectroscopic means, including two dimensional (2D)-NMR, mass spectrometry and circular dichroism. A possible metabolic pathway was proposed on the basis of their structures and time course experiments monitored by thin-layer chromatography. Furthermore, a bacterial strain responsible for the transformation of (+)-pinoresinol to (+)-lariciresinol was isolated from a human fecal suspension and identified as Enterococcus faecalis strain PDG-1.