chamissonolide and helenalin

The biological activities of sesquiterpene lactones have been attributed to their reactivity with the cysteine residues of functional proteins forming covalent bonds via Michael type addition. In the present study we investigated the influence of different L-cysteine (cys) and glutathione (GSH) concentrations on the cytotoxicity of the sesquiterpene lactones (STLs) helenalin, 11alpha,13-dihydrohelenalin acetate and chamissonolide against KB cells. Due to the significantly higher reactivity of the alpha-methylene-gamma-lactone (ML) towards cys as compared with the cyclopentenone (CP) site at physiological pH, addition of 20, 50 and 100 molar equivalents of cys decreased the cytotoxicity of helenalin and chamissonolide, whereas the cytotoxicity of 11alpha,13-dihydrohelenalin acetate remained unaffected. In contrast, the influence of GSH addition on the cytotoxicity of 11alpha,13-dihydrohelenalin acetate depends on the concentration of GSH added. Concentration-effect curves obtained for chamissonolide and GSH resembled the decline in cytotoxicity after cys addition. Helenalin showed a biphasic shape of the concentration-effect curve for the 100:1 GSH/helenalin ratio resembling at higher doses the chamissonolide and in lower doses the 11alpha,13-dihydrohelenalin acetate curve at 50-fold excess. These results can be explained by the different reactivity and equilibrium conditions for thiol addition of the two reactive centers of bifunctional STLs in cellular test systems and verified a clear correlation between the different reactivity of their electrophilic centers and the observed biological effects in in-vitro cell systems.

Topics: Anti-Inflammatory Agents, Non-Steroidal; Antineoplastic Agents; Cell Survival; Cysteine; Drug Interactions; Glutathione; Humans; KB Cells; Lactones; Sesquiterpenes; Sesquiterpenes, Guaiane; Tumor Cells, Cultured

The reactivity of the two potential Michael addition sites of the helenanolide-type sesquiterpene lactone helenalin towards the physiological thiols glutathione (GSH) and cysteine (cys) in aqueous solution was investigated by 1H NMR spectroscopic experiments. In the presence of one molar equivalent of GSH, the reaction was shown to occur with high regio- and stereoselectivity at the beta-position of C-2 in the cyclopentenone ring. Addition to the exocyclic methylene group at the lactone ring was found to occur in the presence, of GSH in molar ratios over 1:1, but proceeded at a rate 10 times smaller than at C-2 leading to the 2 beta,13(11 beta)-bis-glutathionyl adduct. In contrast, addition of free cys highly favoured the exocyclic methylene group. Addition of GSH to the cyclopentenone of 11 alpha, 13-dihydrohelenalin (plenolin) showed the same characteristics as observed with helenalin while 2 alpha-acetoxy-2,3-dihydro-4 beta H-helenalin (chamissonolide) did not form an adduct when incubated with an equimolar amount of GSH. Explanations for the observed differences in reactivity of the two potential reaction sites based on MO computations are given and implications for the biological activity of this type of sesquiterpene lactones are discussed.

Topics: Antineoplastic Agents, Phytogenic; Binding, Competitive; Cysteine; Glutathione; Magnetic Resonance Spectroscopy; Models, Molecular; Sesquiterpenes; Sesquiterpenes, Guaiane; Stereoisomerism; Structure-Activity Relationship; Toxins, Biological

Alcoholic extracts prepared form Arnicae flos, the collective name for flowerheads from Arnica montana and A. chamissonis ssp. foliosa, are used therapeutically as anti-inflammatory remedies. The active ingredients mediating the pharmacological effect are mainly sesquiterpene lactones, such as helenalin, 11alpha,13-dihydrohelenalin, chamissonolid and their ester derivatives. While these compounds affect various cellular processes, current data do not fully explain how sesquiterpene lactones exert their anti-inflammatory effect. We show here that helenalin, and, to a much lesser degree, 11alpha,13-dihydrohelenalin and chamissonolid, inhibit activation of transcription factor NF-kappaB. This difference in efficacy, which correlates with the compounds' anti-inflammatory potency in vivo, may be explained by differences in structure and conformation. NF-kappaB, which resides in an inactive, cytoplasmic complex in unstimulated cells, is activated by phosphorylation and degradation of its inhibitory subunit, IkappaB. Helenalin inhibits NF-kappaB activation in response to four different stimuli in T-cells, B-cells and epithelial cells and abrogates kappaB-driven gene expression. This inhibition is selective, as the activity of four other transcription factors, Oct-1, TBP, Sp1 and STAT 5 was not affected. We show that inhibition is not due to a direct modification of the active NF-kappaB heterodimer. Rather, helenalin modifies the NF-kappaB/IkappaB complex, preventing the release of IkappaB. These data suggest a molecular mechanism for the anti-inflammatory effect of sesquiterpene lactones, which differs from that of other nonsteroidal anti-inflammatory drugs (NSAIDs), indomethacin and acetyl salicylic acid.

Topics: Anti-Inflammatory Agents, Non-Steroidal; Antineoplastic Agents, Phytogenic; Arnica; B-Lymphocytes; Blotting, Western; DNA-Binding Proteins; Electrophoresis, Polyacrylamide Gel; Gene Expression Regulation; HeLa Cells; Humans; I-kappa B Proteins; Jurkat Cells; NF-kappa B; NF-KappaB Inhibitor alpha; Phosphorylation; Plant Extracts; Plants, Medicinal; Sesquiterpenes; Sesquiterpenes, Guaiane; Structure-Activity Relationship; T-Lymphocytes; Transfection