Isolation, characterization and determination of minor artichoke (Cynara scolymus L.) leaf extract compounds

Abstract

Artichoke (Cynara scolymus L.) and artichoke leaf extracts (ALE) have a long history as a traditional part of the Mediterranean diet as well as in folk medicine for the treatment of dyspeptic disorders. Although several biological mechanisms of action have been suggested, e.g. increased biliary secretion leading to an increased cholesterol elimination and/or inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity resulting in a decreased cholesterol biosynthesis, convincing and conclusive human studies investigating the blood cholesterol lowering properties of artichoke or ALE are currently limited. The aim of the present study was to isolate, characterize and determine minor artichoke compounds with regard to their blood cholesterol lowering potential, bitter taste sensation and antioxidant potential. Liquid chromatographic isolation techniques (Sephadex LH-20) in combination with analytical methods (HPLC-DAD-MS and HPLC-DAD) were successfully employed to separate, characterize, and quantify minor artichoke compounds. In commercially available ALE the following compounds were identified: 8-deoxy-11-hydroxy-13-chlorogrosheimin, cryptochlorogenic acid, chlorogenic acid, neochlorogenic acid, cynarin, cynaratriol (tentatively), grosheimin, 8-deoxy-11,13-dihydroxygrosheimin, luteolin-7-O-rutinoside, luteolin-7-O-glucoside, and cynaropicrin. Most of these compounds were liquid chromatographically described for the first time. The concentration of essential ALE compounds, namely chlorogenic acid, cynarin, and luteolin-7-O-glucoside, was in the range of 0.35–18.34, n.d.-1.02, 0.04 – 10.65 mg/g ALE, respectively. Cynaropicrin, the predominant bitter ALE principle, was present at concentrations between <0.06 and 22.6 mg/g ALE. Rancimat assay revealed an equivocal picture with respect to the antioxidant (AOX) properties of ALE dissolved in sunflower oil: four extracts showed a effect, while three ALE had an antioxidative effect and one extract showed no effect at all at concentration between 500 and 4000 mg/kg (compared to refined sunflower oil). However, all investigated individual artichoke compounds – chlorogenic acid, cynarin, luteolin, luteolin-7-O-glucoside – showed a remarkable antioxidative effect, chlorogenic acid being the strongest AOX compound. Moreover, chlorogenic acid showed a strong, dose-dependent linear HMG-CoA reductase inhibitory effect at concentrations between 5 and 50 mg/ml. Luteolin and luteolin-7-O-glucoside showed an even stronger inhibitory effect at 10 mg/ml (relative HMG-CoA reductase activity: 2.4% and 6.5%, respectively compared to 26.5% activity after chlorogenic acid treatment). All studied commercially available ALE showed a moderate inhibitory effect at 10 mg/ml.