EFFECTS OF FEVERFEW EXTRACT AND PARTHENOLIDE ON PLATELET SECRETION.

Feverfew (Tanacetum parthenium) is used for prophylaxis of migraine and it had been suggested that the plant may have antithrombotic potential. We have prepared extracts from the leaves of feverfew and have demonstrated inhibition of ¹⁴C-5HT secretion in platelet-rich plasma induced by the phorbol ester PMA, l-oleoyl-2-acetyl-sn-glycerol (OAG), arachidonic acid, the thromboxane analogue U46619, adrenaline, collagen and ADP. The effects of a solution of parthenolide (an∝-methylenebutyro-lactone isolated from feverfew) were determined in parallel. Both feverfew extract (FE) and parthenolide inhibited ¹⁴C-5HT release in a concentration-dependent manner and the effectiveness depended on the nature of the aggregating agent used. Both FE and parthenolide were most effective as inhibitors of the secretion induced by PMA and OAG. When we compared the concentrations of FE and parthenolide which gave 50% inhibition of secretion for all the agents tested, a good correlation was found (r= 0.936). Further studies showed that feverfew extract and parthenolide inhiMt release of β-thromboglobulin from platelets as well as ¹⁴C-5HT. FE did not cause liberation of LDH. Inhibition of secretion by FE appears to be irreversible since washing platelets after treatment did not restore secretory activity.

The structure of parthenolide suggests that it can alkylate sulphydryl (SH) groups. When agents containing SH groups (e.g. cysteine) were added to FE, anti-secretory activity was reduced. We also obtained a considerable decrease in the number of acid-soluble SH groups in platelets treated with feverfew extract or parthenolide at concentrations which inhibit secretion. However there was a less marked decrease in the number of acid-insoluble SH groups. FE itself does not induce formation of disulphide-linked proteins but such proteins were formed when platelets were activated in the presence of FE, probably as a result of decreased glutathione levels.

We conclude that parthenolide or parthenolide-like compounds are responsible for the anti-secretory effects of FE, and that alkylation of sulphydryl groups in platelets may be involved.