Article

Bioactive compounds from Iceland moss

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Abstract

Pharmacological investigations of the lichen Cetraria islandica (L.) Ach. have shown that polysaccharides as well as low molecular weight constituents exhibit significant biological activity. A polysaccharide with a backbone of (1→6)-linked a-D-mannopyranosyl and a-D-(1→6)-galactopyranosyl units has been isolated from an alkali extract of Iceland moss. The galactomannan (mean Mr = 18 kdalton) exhibited pronounced enhancement of phagocytosis in both in vitro and in vivo assays. In addition, several polysaccharide fractions, isolated from a hot aqueous extract of Iceland moss by ethanol fractionation and ion-exhange chromatography, exerted significant activity in several immunological assays. The fractions showed in vitro anticomplementary activity, pronounced enhancement of in vitro granulocytic phagocytosis and a significant increase in the rate of colloidal carbon elimination in the in vivo carbon clearance test. An a-(1→3 )-(1-→4)-glucan (mean Mr = 2,000 kdalton) has been isolated in pure form from two of the aqueous fractions. Of low molecular weight constituents, the aliphatic a-methylene-y-lactone (+)-protolichesterinic acid has exhibited prominent activity in several in vitro biological assays. With reference to the traditional use of Iceland moss, inhibitory effects of plant constituents on arachidonate metabolism and Helicobacter pylori have been studied. In both cases activity was detected and attributed to protolichesterinic acid, which exhibited dose-dependent inhibitory effects (IC5O = 20 μM) on the enzyme 5-lipoxygenase and an MIC range of 16-64 µg/ml (n = 35) against H. pylori. Protolichesterinic acid has furthermore been shown to have marked anti-proliferative activity against two breast cancer cell lines (T-47D, ZR-75-1) and the leukemia cell line K-562 (ED50 = 3-15 µM) without affecting normal lymphocytes and human skin fibroblasts .

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The aliphatic α-methylene-γ-lactone (+)-protolichesterinic acid (1), isolated from Cetraria islandica, has been shown to exhibit inhibitory effects on the enzyme 5-lipoxygenase in an in vitro assay in which porcine leucocytes are used as a source of the enzyme system. The isomeric compounds (+)-lichesterinic acid (2) and (-)-lichesterinic acid (4), prepared from (+)-protolichesterinic- and (-)-allo-protolichesterinic acids, respectively, exhibited anti-5-lipoxygenase activity of the same order of magnitude. (+)-Methyl lichesterinate (3) was, however, inactive. It was shown that despite its lipophilic nature, protolichesterinic acid is extractable into an aqueous medium, the concentration being dependent on the length of extraction.
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Several lichen species have been used traditionally as medicinal plants. It has previously been shown that two low-molecular-weight lichen metabolites, lobaric acid isolated from Stereocaulon alpinum Laur. and protolichesterinic acid isolated from Cetraria islandica L. (Ach.), have in-vitro inhibitory effects on arachidonate 5-lipoxygenase. We have studied the effects of these compounds on cultured cells from man, including three malignant cell-lines (T-47D and ZR-75-1 from breast carcinomas and K-562 from erythro-leukaemia), as well as normal skin fibroblasts and peripheral blood lymphocytes. Both test substances caused a significant reduction in DNA synthesis, as measured by thymidine uptake, in all three malignant cell-lines; the dose inducing 50% of maximum inhibition (ED50) was between 1.1 and 24.6 μg mL−1 for protolichesterinic acid and between 14.5 and 44.7 μg mL−1 for lobaric acid. The breast-cancer cell-lines were more sensitive than K-562. The proliferative response of mitogen-stimulated lymphocytes was inhibited with a mean ED50 of 8.4 μg mL−1 and 24.5 μg mL−1 for protolichesterinic acid and lobaric acid, respectively. These concentrations are of the same order of magnitude as the IC50 values in the 5-lipoxygenase assay. Significant cell death (assessed by the MTS (3–4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay and trypan blue exclusion) occurred in the three malignant cell-lines at protolichesterinic acid and lobaric acid concentrations above 20 and 30 μg mL−1, respectively. In K-562 morphological changes consistent with apoptosis were detected. Up to 38% cell death was observed at 20 μg mL−1 for protolichesterinic acid and 15 μg mL−1 for lobaric acid in mitogen-stimulated lymphocytes but unstimulated lymphocytes were clearly less sensitive. In contrast, the DNA synthesis, proliferation and survival of normal skin fibroblasts were not affected at doses up to 20 μg mL−1 for protolichesterinic acid and 30 μg mL−1 for lobaric acid. We conclude that the anti-proliferative and cytotoxic effects observed might be related to the 5-lipoxygenase inhibitory activity of protolichesterinic acid and lobaric acid. These results open up the opportunity for future studies of these lichen metabolites with regard to their anti-tumour and anti-inflammatory properties.
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Einige Polysaccharide, die aus Flechten isoliert wurden, hemmen das Wachstum des Sarkoms-180 in Mäusen und verursachen in vielen Fällen vollständige Regression der Tumoren.
Article
A new alkali-soluble polysaccharide has been isolated from Iceland moss, Cetraria islandica (L.) Ach., by ethanol fractionation, ion-exchange chromatography, and gel filtration. The mean M(r) was estimated to be 18,000. Sugar and methylation analysis, partial hydrolysis, and 13C-NMR spectroscopy showed the polysaccharide to be a branched galactomannan with a backbone composed of two structural elements; (1-->6)-linked alpha-D-mannopyranosyl and alpha-D-(1-->6)-galactopyranosyl units. The polysaccharide showed pronounced immunostimulating activity in an in vitro phagocytosis assay and in the in in vivo carbon clearance assay.
Article
With reference to the traditional use of Cetraria islandica (Iceland moss) for relief of gastric and duodenal ulcer, plant extracts were screened for in vitro activity against Helicobacter pylori. (+)-Protolichesterinic acid, an aliphatic alpha-methylene-gamma-lactone, was identified as an active component. The MIC range of protolichesterinic acid, in free as well as salt form, was 16 to 64 micrograms/ml.
Article
A polysaccharide, Ci-3, resembling isolichenan except with a much higher degree of polymerization, has been isolated from the water extract, as well as from the alkali extract, of the lichen Cetraria islandica (L.) using ethanol fractionation, dialysis, ion-exchange chromatography and gel filtration. The mean M(r) of Ci-3 was determined to be 2000 kD, compared to 6-8 kD reported for isolichenan. The structure of Ci-3 was elucidated and found to be composed of (1-->3)- and (1-->4)-alpha-D-glucopyranosyl units in the ratio of 2:1, using methanolysis, methylation analysis, optical rotation and NMR spectroscopy. The immunomodulating activity of Ci-3 was tested in an in vitro phagocytosis assay and anti-complementary, and proved to be active in both tests.