| Description |
Extracts from artichoke (Cynara scolymus L.) or cardoon (Cynara cardunculus L., Asteraceae), are widely used in phytotherapy as choleretic, hypocholesterolemic and hepatoprotective agents (Kraft, 1997). The cholesterol-lowering effect of artichoke extracts was confirmed by numerous animal experiments and recently by a controlled clinical trial. The possible mechanism of hypocholesterolemic activity involves choleretic action, reduction of cholesterol biosynthesis and inhibition of low density lipoprotein oxidation (Pittler and Ernst, 1998). The antiatherosclerotic and antihepatotoxic activities can be mediated by antioxidative action of the artichoke extract. These activities have been ascribed to the phenolic compounds present in the extract. According to HPLC analysis, the methanol extract of C. cardunculus leaves contained three main phenolic components, 5-caffeoylquinic acid (chlorogenic acid), 1,5-dicaffeoylquinic acid (1,5-DiCQA) and flavonoid luteolin-7-O-glucoside. However, caffeoylquinic acids can undergo isomerisation or hydrolysis in aqueous solutions. Thus, 1,5-dicaffeoylquinic acid forms 1,3-dicaffeoylquinic acid, named cynarin, which was isolated as the active principle of artichoke by Panizzi and Scarpati in 1954. More recent discoveries point to a role for the other phenolics, above all luteolin, in the inhibition cholesterol biosynthesis (Gebhardt, 1998) and retardation of LDL oxidation (Brown and Rice-Evans, 1998). Nevertheless, the comparison of the antiradical activity of all the main phenolics present in the artichoke leaf extract has not been examinated yet. We isolated 1,5-DiCQA (Slanina et.al., 1999), cynarin, luteolin and luteolin-7-O-glucoside from the methanol extract of the C. cardunculus leaves (Slanina, 1999). These phenolic compounds together with chlorogenic and caffeic acid were assayed for the antiradical activity by 1,1-diphenyl-2-picrylhydrazyl (DPPH). The antiradical effect of all phenolic acids and flavonoids was stronger than that of ascorbic acid (EC50 = 10.3 umol/L). The ability to scavenge the free stable DPPH radical increased with the number of the catechol groups and also with the number of other phenolic groups in the order: caffeic acid (EC50 = 5.8 umol/L) < chlorogenic acid (5.0 umol/L) < luteolin (4.8 umol/L) < luteolin-7-glucoside (4.3 umol/L) < cynarin (3.9 umol/L) < 1,5-DiCQA (2.8 umol/L). The stronger antiradical acvtivity of 1,5-DiCQA than that of cynarin may be rationalized by the presence of one equatorial caffeoyl group in 1,5-DiCQA, whereas cynarin has both axial caffeoyl groups. Comparing the scavenging activities, 1 mole of ascorbic acid reacted with approximately 2 moles of DPPH radical and 1 mole of 1,5-DiCQA scavenged about 6 moles of the radical. This is in good accordance to resultes obtained with 3,5-DiCQA (Ohnishi et.al., 1994). Our findings show that 1,5-DiCQA is the important antioxidant component of C. cardunculus leaves owing to its strong antiradical activity and the high content in the leaves.
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