Allium ursinum L.: bioassay-guided isolation and identification of a galactolipid and a phytosterol exerting antiaggregatory effects.

AIMS

We wanted to investigate the possible antithrom botic effects and elucidate the chemical identity of the active principles involved in inhibitory effects against adenosine diphosphate(ADP)-induced aggregation of human platelets by wild garlic, Allium ursinum L.

METHODS

For this purpose, a bioassay-guided isolation procedure was used followed by spectrometric identification of pure active compounds. For the bioassay, blood was taken from healthy human volunteers and platelet-rich plasma was prepared for turbidimetric platelet aggregation tests. Platelet-rich plasma, stimulated with 20 μ mol/l of ADP, was treated with extracts of different polarities, fractions and isolated single compounds from A. ursinum. The extracts were investigated by thin-layer chromatography(TLC), HPLC, mass spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and 1/2-dimensional (1)H/(13) C-nuclear magnetic resonance (NMR) spectroscopic techniques.

RESULTS

Fresh A. ursinum leaves were extracted with ethanol, which was the potent form that effectively inhibited ADP-induced aggregation of human platelets. Thisethanolic extract was subjected to liquid-liquid partition. Whilst the aqueous phase, containing the moiety of cysteine sulphoxide and thiosulphinate derivatives, showed only weak activity on platelet aggregation, the ethyl-acetate and particularly the chloroform partitions showed the high estaggregation-inhibiting potency. Thus, in our bioassay, the effects of alliins/allicins could be neglected. The chloroform phase, possessing the strongest activity, was separated into 28 fractions by gradient-elution open column chromatography on silica gel. The most active fractions 11–17 were separated again, yielding 10 subfractions. This afforded 1,2-di-O-α-linolenoyl-3-O-β-D-galactopyranosyl-sn-glycerol and β-sitosterol-3-O-β-D-glucopyranoside, the structures of which were determined by ESI-MS and 1/2-dimensional (1)H/(13) CNMR spectroscopic techniques. Furthermore, the minute amounts of volatile oil of A. ursinum leaves obtained by steam distillation according to Ph. Eur. could be evaluated asa third aggregation-inhibiting principle.

CONCLUSION

In our study, for the first time, 2 active, non-sulphur-containing constituents of wild garlic, namely a galactolipid and a phytosterol,could be identified exhibiting inhibitory action on ADP-induced aggregation in human blood platelets. As a major constituent, the galactolipid, 1,2-di-O-α-linolenoyl-3-O-β-D-galactopyranosyl-sn-glycerol, not yet found in Allium sp., appears as a new, highly useful marker substance for A. ursinum drugs, or their pharmaceutical or food preparations,as shown by our orientating TLC analyses.