Bioactive compounds from Iceland moss

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 M _r = 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 M _r = 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 (IC_5O = 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 .