High anti‐inflammatory activity of harpagoside‐enriched extracts obtained from solvent‐modified super‐ and subcritical carbon dioxide extractions of the roots of Harpagophytum procumbens

Solvent‐modified carbon dioxide extractions of the roots of Harpagophytum procumbens have been investigated with respect to extraction efficiency and content of harpagoside, and compared with a conventional extract. The effects of pressure, temperature, type and concentration of the modifier have been examined. Two extraction steps were necessary in order to achieve high anti‐inflammatory harpagoside‐enriched extracts. The first extraction step was carried out in the supercritical state using carbon dioxide modified with n ‐propanol to remove undesired lipophilic substances. The main extraction was performed either in the supercritical or in the subcritical state with carbon dioxide modified with ethanol. The supercritical fluid extraction resulted in extracts containing up to 30% harpagoside. The subcritical extracts showed a harpagoside content of ca. 20%, but the extraction yield was nearly three times greater compared with supercritical conditions. The total harpagoside recovery resulting from the sum of the extract and the crude drug residue was greater than 99% in all experiments. The conventional extract and two carbon dioxide extracts were tested for in‐vitro inhibition of 5‐lipoxygenase or cyclooxygenase‐2 biosynthesis. Both carbon dioxide extracts showed total inhibition on 5‐lipoxygenase biosynthesis at a concentration of 51.8 mg/L. In contrast, the conventional extract failed to show any inhibition of 5‐lipoxygenase biosynthesis. Copyright © 2005 John Wiley & Sons, Ltd.