Differential and Stereoselective In Vitro Cytotoxicity of Eremophilane Sesquiterpenes of Petasites hybridus Rhizomes in Rat Hepatocytes

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

References

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