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DOI: 10.1055/s-0030-1250112
© Georg Thieme Verlag KG Stuttgart · New York
Differential and Stereoselective In Vitro Cytotoxicity of Eremophilane Sesquiterpenes of Petasites hybridus Rhizomes in Rat Hepatocytes
Publication History
received Dec. 28, 2009
revised June 5, 2010
accepted June 10, 2010
Publication Date:
22 July 2010 (online)

Abstract
We tested two CO2 extracts of Petasites hybridus L. rhizomes, A (rich in furanoeremophilanes) and B (rich in petasins), for in vitro cytotoxicity in rat hepatocytes by means of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay (EC50 values of 0.64 mg/mL for A and 0.32 mg/mL for B). Eight eremophilane sesquiterpene lactones (SL) (1–8) and one petasin (9) isolated from A were nontoxic or showed moderate cytotoxicity. The presence and type of the ester side chain most probably control the extent of cytotoxicity of the eremophilanolides. (8R)-2-[(angeloyl)oxy]eremophil-7(11)-en-12,8-olide (1) damaged the hepatocytes most. The 8α-stereoisomers of both 8-H epimeric couples of the 2-angeloyloxy- and 2-methacroyloxy-esters seem to be more cytotoxic (up to approx. 10-fold) than the corresponding 8β-H stereoisomers. Moreover, the results of the MTT assay depended on the cell density being more pronounced with both 8α-stereoisomers. Further investigations were conducted to study the influence of the stereochemistry on cell respiration, energy metabolism, and membrane integrity [release of lactate dehydrogenase (LDH)] with both couples of the 2-angeloyloxy- and 2-methacroyloxy-esters. In the LDH-leakage assay, (8R)-2-[(methacroyl)oxy]eremophil-7(11)-en-12,8-olide (2) was the most toxic eremophilane. The stereoselectivity of cell damage of some SL points to a specific, yet unidentified molecular cytotoxicity target.
Key words
cytotoxicity - hepatocytes - Petasites hybridus - Asteraceae - eremophilane sesquiterpenes - stereoisomerism
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